Colloquia are Wednesdays at 4:00 p.m. in DUAN G1B20, unless otherwise noted.

Coffee, tea and cookies will be available before regular colloquia beginning at 3:45 p.m. in DUAN G1B31.

January 18 — "Gravitational Waves, Colliding Black Holes, And Tornadoes In Space-Time: The Dawn Of A New Astronomy"

  • Presenter: David Reitze, LIGO Laboratory and University of Florida, Gainesville
  • Host: Henry Kapteyn
  • Abstract: The first direct detections of gravitational waves in late 2015 were made possible by a forty year experimental campaign to design, build, and operate LIGO, the Laser Interferometer Gravitational-wave Observatory. In this colloquium, I’ll cover gravitational waves and what makes them so difficult to detect and at the same time such powerful and unique probes of the universe. I’ll also give a flavor of the somewhat complicated history of how LIGO was conceived and built. Most of the presentation will focus on the interferometers, the LIGO detections and their astrophysical implications. Time permitting, I’ll give a preview of where LIGO intends to go in the next decade and beyond.  

January 25 — "15 Years of PhET Interactive Simulations: Cycles of Innovation, Learning, and Impact"

  • Presenter: Kathy Perkins, University of Colorado, Boulder
  • Host: John Price
  • Abstract: With a collection of 134 interactive simulations for teaching science and math, and over 100 million simulation uses per year worldwide, the PhET Interactive Simulations project has come a long way since its beginning in 2002. Founded by our colleague Carl Wieman as the “Physics Education Technology” project, his vision was to make physics engaging and accessible for all learners by tapping into a natural curiosity about real world phenomena. The journey from 2002 to today has included many cycles of innovation and learning as PhET expanded from physics to chemistry to math, from college to middle school, and from a local resource to an international mainstay. We will reflect on these past cycles – the challenges and the solutions – and how physics and the physicist’s perspective has shaped and advanced our work throughout. We will also look ahead to what’s on the horizon for PhET – bringing science inquiry to students with disabilities, advancing assessment of science practices, transforming middle school math, and building a sustainable business model.

**Special Colloquium** Monday, January 30 — "Unlocking neutrino mysteries with the NOvA experiment"

  • Presenter: Christopher Backhouse, California Institute of Technology
  • Host: Kevin Stenson
  • **NOTE SPECIAL LOCATION: DUAN G130
  • Abstract: The 2015 Nobel Prize in Physics was awarded for the discovery of the phenomenon of neutrino oscillations, which implies that neutrinos are not massless as we had previously believed. This raises a wealth of new and intriguing questions. What is the ordering of the neutrino mass states? Might they violate matter/antimatter symmetry? What structure, if any, does the neutrino mixing matrix have? The NOvA experiment directly addresses these questions by measuring changes undergone by a powerful neutrino beam over an 810 km baseline, from its source at Fermilab, Illinois to a huge 14 kton detector in Ash River, Minnesota. I will give a brief overview of neutrino oscillations, then present our latest results, their implications, and prospects for the future.

February 1 — "The 1,358,954,496 Matrix Elements to Get From SUSY Diff Eq's to Pictures, Codes, Card Games, Music, Computers, and Back Again"

  • Presenter: S. James Gates, University of Maryland
  • Host: Clifford Bridges
  • Abstract: In this presentation a discussion is given of a recent derivation of a supersymmetrical QM representation spectrum that took some surprising twists and turns along the way.

February 8 — "Quarks of Many Colors"

  • Presenter: Tom DeGrand, University of Colorado Boulder
  • Host: John Price
  • Abstract: Numerical simulation of quantum chromodynamics  (QCD) is a successful way to compute the properties of strongly interacting particles from first principles. However, it doesn't give much insight into why the numbers are what they are. Long ago Hooft argued that QCD could be understood most simply when the “three'” of the three colors was taken to be a large number. But nobody could compute anything like a reduced matrix element with this idea. Recently, people have begun to marry these two stories.  I'll tell you a bit about them both, put them together, and  see what we find. Remarkable regularities emerge.

Special Colloquium — Monday, February 13 "Physics at the LHC: Why and How to go Beyond the Higgs Discovery"

  • Presenter: John Alison, University of Chicago
  • NOTE SPECIAL LOCATION: DUAN G130
  • Host: Kevin Stenson
  • Abstract: The Standard Model (SM) of particle physics is a spectacularly successful theory that is known to be fundamentally incomplete.  The recent discovery of the Higgs boson at the Large Hadron Collider is, on one hand, the final missing piece of the SM and, on the other, a window into what lies beyond.  I will discuss the motivations and experimental challenges of searching for physics beyond the SM at the LHC.  Emphasis will be placed on using the Higgs boson as a probe of new physics in processes involving pairs of Higgs bosons.

February 15 — "Looking for Fossils of the Big Bang in Molecular Spectra"

  • Presenter: Eric Cornell, JILA and University of Colorado, Boulder
  • Host: John Price
  • Abstract: How can you learn about the early moments of the universe? How can you discover evidence for new sub-atomic particles? We usually think of ever-more exotic telescopes, or of ever-larger particle accelerators. I will talk about the third leg of the stool: precision measurement. We will see that the humble two-atom molecule should be thought of as an ultrahigh electric-field laboratory.

Special Colloquium — Monday, February 20 "Strategies for searches of physics beyond the Standard Model in the XXI century"

  • Presenter: Manuel Franco Sevilla, University of California, Santa Barbara
  • NOTE SPECIAL LOCATION: DUAN G130
  • Host: Kevin Stenson
  • Abstract: At the end of the XIX century, Lord Kelvin summarized a widespread feeling among physicists by saying that "physics is essentially complete, save for two little clouds". The "clouds" he was (apocryphally) referring to were the puzzling results from two measurements, the Michelson-Morley experiment and the Black-body spectrum, whose explanations ushered in an unprecedented era of discoveries that stretched throughout most of the XX century. After the culmination of the Standard Model in the 70's, the field of particle physics has found itself in a similar situation. Today, the "clouds" guiding the searches for physics beyond the Standard Model are issues like dark matter or the hierarchy problem. Using SUSY searches at CMS and the measurement of B->D(*)TauNu decays at BaBar as models, I will give an overview of some of the main strategies that are being followed in the quest to find new physics in the XXI century.

February 22 — "The Difficult Search for CP Violation in Neutrinos"

  • Presenter: Michael Wilking, Stony Brook University
  • Host: Kevin Stenson
  • Abstract: To observe CP violation, experiments must make precise, differential measurements of the appearance of electron neutrinos and anti-electron neutrinos. This requires unprecedented control of systematic uncertainties, and, in particular, an understanding of neutrino-nucleus interactions that is beyond the capabilities of existing theoretical models. The resulting "neutrino energy measurement problem" that will be confronted by current and future long-baseline neutrino oscillation experiments, as well as potential experimental solutions, will be discussed.

March 1 — "Searching for Supersymmetry at the LHC"

  • Presenter: Keith Ulmer, Texas A&M
  • Host: Kevin Stenson
  • Abstract: The Large Hadron Collider (LHC) at CERN currently provides the highest energy particle collisions ever produced in a laboratory. These collisions were reconstructed and analyzed by the CMS and ATLAS experiments to claim the discovery of the Higgs Boson in 2012, thus completing the standard model of particle physics. This talk explores what's next for the LHC, including the implications of the Higgs discovery on the search for new physics beyond the standard model. In particular, such open questions as the nature of dark matter and the gauge hierarchy problem may find eloquent solutions in supersymmetry, a proposed new symmetry of nature relating fermions and bosons. I will discuss the current state of experimental searches for supersymmetry at CMS, including the near term prospects for discovery, and will conclude with an example of the innovative new technological solutions being explored to continue the hunt for new physics into the High Luminosity LHC era set to begin in the coming decade.

March 8 — "Searching for axion and hidden photon dark matter with lumped element electromagnetic resonators and SQUIDs"

  • Presenter: Kent Irwin, Stanford University
  • Host: Nils Halverson
  • Abstract: About 85% of the matter in the universe is made up of an unknown "dark" component that is mostly non-baryonic. For several decades, searches for this mysterious substance has principally focused on one candidate particle: the WIMP. Superconducting Quantum Interference Devices (SQUIDs) have played an important role in these searches, which have successfully ruled out significant phase space for WIMP dark matter. Recently, there has been a surge in theoretical interest in ultra-light-field dark matter, including QCD axions (spin 0 bosons) and hidden photons (spin 1 bosons). The Dark Matter Radio (DM Radio) is a tunable superconducting high-Q lumped-element resonator also using SQUIDs for detection. I will discuss the motivation, status and prospects for the DM Radio experiment in searching for both axions and hidden photons, and the remarkable phase space that DM Radio will search over the next several years.

March 15 — "Tunable Materials and Metasurfaces – from Quantum to Perfect"

  • Presenter: Harry Atwater, California Institute of Technology
  • Host: Scott Diddams
  • Abstract: Tuning the Fermi level and complex dielectric function of low-dimensional nanophotonic structures including layered materials and nanoantenna arrays enables scientific exploration of quantum materials such graphene, phosphorene and topological insulators and, as well applications including electronic phase and amplitude modulators for the near infrared (conducting oxides) and mid infrared (graphene). We discuss light-matter interactions in materials and report dynamically tunable metasurfaces exhibiting >π phase modulation and ‘perfect’ absorption approaching 100%.

March 22 — "High-Capacity Optical Communications using Multiplexing of Multiple Orbital-Angular-Momentum Beams"

  • Presenter: Alan Willner, University of Southern California
  • Host: Scott Diddams
  • Abstract: Optical communications has historically experienced tremendous capacity growth by multiplexing many channels and transmitting them simultaneously. Recently, the community has turned to research the possibility of space-division-multiplexing (SDM) as the next domain to exploit, and multiple spatially overlapping orthogonal modes can achieve a subset called mode-division-multiplexing (MDM). Indeed, the ability to multiplex multiple data-carrying modes over the same physical medium represents the potential for increasing system capacity and spectral efficiency.
    Generating different amounts of orbital-angular-momentum (OAM) on different optical beams has emerged as a technique for such mode multiplexing. A beam can carry OAM if its phase front twists in a helical fashion as it propagates, and the amount of OAM corresponds to the number of 2*pi phase shifts that occur in the azimuthal direction. Each OAM beam is orthogonal to other beams, and such beams can be efficiently multiplexed, transmitted, and demultiplexed with little inherent crosstalk. This presentation will explore the achievements of and challenges to OAM-based optical and millimeter-wave communication systems, including transmission, turbulence compensation, and link design.

March 29 — Spring Break; No Colloquium

April 5 — "Thermoelectrics and Thermoelectric Materials"

  • Presenter: David Singh, University of Missouri
  • Host: Gang Cao
  • Abstract: Thermoelectric devices are used for the conversion of thermal and electrical energy. They offer a number of advantages over competing technologies including scalability to small sizes and temperature differences, simple reliable designs and often low cost. However, these devices have not seen wide application in energy applications due to their limited conversion efficiency. This is a consequence of the limited performance of current thermoelectric materials, which can be characterized by a dimensionless figure of merit, ZT=σS2T/κ. There is no known fundamental limit on ZT. However, the combination of transport parameters entering ZT is a combination that does not occur in ordinary materials. This talk presents an overview of ZT and discusses strategies for optimizing ZT as well as recent results that point to ways of identifying new high ZT compositions. An important finding is that electronic structure plays a remarkably subtle role in thermoelectric performance that can however be simply visualized in terms of iso-energy surfaces. Finally, a connection is drawn between topological insulators and high ZT thermoelectrics, explaining the overlap between these two interesting materials classes. Characteristics that can be used to identify new thermoelectric compositions are presented and discussed.

April 12 — "Structure and Dynamics with Ultrafast Electron Microscopes… or how to make atomic-level movies of molecules and materials"

  • Presenter: Brad Siwick, McGill University
  • Host: John Price
  • Abstract: In this talk I will describe how combining ultrafast lasers and electron microscopes in novel ways makes it possible to directly ‘watch’ the time-evolving structure of condensed matter on the fastest timescales open to atomic motion.  By combining such measurements with complementary (and more conventional) spectroscopic probes one can develop structure-property relationships for materials under even very far from equilibrium conditions.

    I will give several examples of the remarkable new kinds of information that can be gleaned from such studies and describe how these opportunities emerge from the unique capabilities of the current generation of ultrafast electron microscopy instruments.  For example, in diffraction mode it is possible to identify and separate lattice structural changes from valence charge density redistribution in materials on the ultrafast timescale and to identify novel photoinduced phases that have no equilibrium analogs.   It is also possible to directly probe the strength of the coupling between electrons and phonons in materials across the entire Brillouin zone and to probe nonequilibrium phonon dynamics (or relaxation) in exquisite detail.  In imaging mode, real space pictures of nano- to microstructural evolution in materials at unprecedented spatio-temporal resolution can be obtained. 

    I will assume no familiarity with ultrafast lasers or electron microscopes.

    References

    1. G. Sciani and  R. J. D. Miller, Femtosecond electron diffraction:  Heralding the era of atomically resolved dynamics, Rep. Prog. Phys. 71 (2011) 096101
    2. R. P. Chatelain, V. Morrison, C. Godbout, and B.  J. Siwick, Ultrafast electron diffraction with radio-frequency compressed electron pulses, Appl. Phys. Lett. 101 (2012) 081901.
    3. V. Morrison, R. P. Chatelain, K. Tiwari, A. Hendaoui, M. Chakker and B.  J.  Siwick, A photoinduced metal-like phase of monoclinic vanadium dioxide revealed by ultrafast electron diffraction, Science 346 (2014) 445 – 448.
    4. R. P. Chatelain, V. Morrison, Bart L. M. Klarenaar and B.  J.  Siwick, Coherent and incoherent electron-phonon coupling in graphite observed with radio-frequency compressed ultrafast electron diffraction, Phys. Rev. Lett. 113 (2014) 235502.
    5. L. Nikolova, M. Stern, T. LaGrange, B. Reed, N. Browning, G. H. Campbell, J.-C. Kieffer, F. Rosei and B. J. Siwick, Complex crystallization dynamics in amorphous germanium studied with dynamic TEM. Phys. Rev. B 87 (2013) 064105. 

April 19 — No Colloquium

April 26 — "Building a Proportional Cell: Lessons from Physics"

  • Presenter: Jané Kondev, Brandeis University
  • Host: Loren Hough
  • Abstract: The inside of a living cell is spatially organized into different functional structures called organelles. For example, the nucleus is a membrane bound compartment that contains the cell's DNA, while the cytoskeleton is made up of dynamic protein fibers which allow cells to move and change shape.  

    Gulliver noticed 140 years ago that the size of the cell's nucleus is proportional to the size of the cell. Similar observations have been made about other micron-sale structures within the cell. These experiments suggest that cells measure and control the size of their organelles, and they raise a simple question: How does the cell establish a micron-scale ruler with nothing more at its disposal than nanometer-sized molecules that diffuse around the cell and on occasion bump into each other?  In this talk I will describe quantitative experiments and related theory that are beginning to reveal general principles of how cells control the size of their organelles. 

May 3 — "Imaging the Surface States of a Strongly Correlated Topological Insulator"

  • Presenter: Jennifer Hoffman, Harvard University
  • Host: Dan Dessau and Minhyea Lee
  • Abstract: The prediction and subsequent discovery of robust spin-polarized surface states on topological band insulators has launched a new subfield of physics over the last decade. In the last few years it has been recognized that when topology is combined with strong electron-electron correlations, even more interesting and potentially useful states of matter can arise, such as new topological classifications, fractionalized states, and many-body localization that preserves the topology of the insulating state against thermal destruction. Here we show the first direct proof of a strongly correlated topological insulator. Using scanning tunneling microscopy to probe real and momentum space structure, our measurements on the heavy fermion material SmB6 reveal the evolution of the insulating gap arising from strong interactions. Within the narrow gap, we directly image a dispersing surface state that converges to a Dirac point close to the chemical potential. Our observations present the first opportunity to explore a strongly correlated topological state of matter.

For more information about colloquia this semester, contact: John Price.

Colloquia are Wednesdays at 4:00 p.m. in DUAN G1B20, unless otherwise noted.

Coffee, tea and cookies will be available before regular colloquia beginning at 3:45 p.m. in DUAN G1B31.

August 24 — "NASA’s Juno Mission to Jupiter: What’s Inside the Giant Planet?"

  • Presenter: Fran Bagenal, University of Colorado Boulder
  • Host: Mihaly Horanyi
  • Abstract: Jupiter is a planet of superlatives: the most massive planet in the solar system, rotates the fastest, has the strongest magnetic field, and has the most extensive satellite system of any planet. NASA’s Juno mission was launched in August 2011 and went into orbit over Jupiter’s poles on July 4th this summer.  Juno’s principal goal is to understand the origin and evolution of Jupiter. Underneath its dense cloud cover, Jupiter safeguards secrets to the fundamental processes and conditions that governed our solar system during its formation. As our primary example of a giant planet, Jupiter can also provide critical knowledge for understanding the planetary systems being discovered around other stars. With its suite of science instruments, Juno will investigate the existence of a solid planetary core, map Jupiter's intense magnetic field, measure the amount of water and ammonia in the deep atmosphere, and observe the planet's auroras. Juno will let us take a giant step forward in our understanding of how giant planets form and the role these titans played in putting together the rest of the solar system. In Greek and Roman mythology, Jupiter drew a veil of clouds around himself to hide his mischief. It was Jupiter’s wife, the goddess Juno, who was able to peer through the clouds and reveal Jupiter’s true nature.  Juno is also the first spacecraft to fly over Jupiter’s aurora and will measure both the energetic particles raining down on the planet and the bright “northern & southern lights” they excite.

August 31 — "Cosmic Dust Research at the Colorado Dust Accelerator"

  • Presenter: Tobin Munsat, University of Colorado Boulder
  • Host: John Price
  • Abstract: Cosmic dust grains play a central role in astrophysics and planetary science; the interaction of dust grains with planetary surfaces and atmospheres can drive weathering processes, surface chemistry (for airless bodies), and even atmospheric chemistry on Earth. Dust-detecting instruments can provide insight into the environment where the particles were formed, whether that is the interstellar medium, comets, asteroids, or even ejected from the surfaces of planets and moons. From a basic physics point of view, hypervelocity impact experiments can access extremely high energy density levels. To address many facets of cosmic dust research in the lab, we have recently developed a dust accelerator on the east campus of CU. This is a 3 MV electrostatic linear accelerator which launches particles in the size range of 0.1 to a few micrometers and velocities up to 100 km/s onto a variety of targets. This talk will describe the basic details of the accelerator and provide an overview of several lines of research being carried out by our group.  Specifically, I will discuss hypervelocity impact cratering experiments in thin films, impact experiments into cryogenic (ice) targets, making "shooting stars" in the lab, and the local development of dust detector instruments that have flown to the moon and will soon fly to Jupiter's moon Europa.

September 7 — "The End of Inflation"

  • Giblin Colloquium GraphicPresenter: Tom Giblin, Kenyon College
  • Host: Ethan Neil
  • Abstract: The evidence for a hot, dense, early stage of the Universe is overwhelming.  Setting up a Universe in this hot-dense stage is more of a challenge.  While Cosmic Inflation as a paradigm has been successful at negotiating  the issues of the Hot Big Bang, its conclusion is marked by a cold, empty state that needs to quickly and efficiently reheat.  Violent processes, turbulent phase transitions and non-linear processes characterize this period and might help us shed light on the particle physics of the very young, very energetic early Universe.  I will describe how we have been using large numerical simulations to calculate precision observables that will help to constrain the growing number of early universe scenarios.

 

September 14 — "Apples vs. Oranges: Comparison of Student Performance in a MOOC vs. a Brick-and-Mortar Course"

  • Presenter: Michael Dubson, University of Colorado Boulder
  • Host: John Price
  • Abstract: In the fall of 2013, my colleagues and I taught the calculus-based introductory physics course to 800 tuition-paying students at the University of Colorado at Boulder. At the same time we taught a free massive open online course (MOOC ) version of the same course, through Coursera.com. The initial enrollment in the MOOC was 10,000 students, of whom 255 completed the course. Students in both courses received identical lectures with identical embedded clicker questions, identical homework assignments, and identical timed exams. We present data on participation rates and exam performance for the two groups. We find that the MOOC is like a drug targeted at a very specific population. When it works, it works well, but it works for very few students. This MOOC worked well for older, well-educated students, who already had a good understanding of Newtonian mechanics.

Ramanujan PortraitSeptember 21 — "Tragic tale of the mathematical genius Ramanujan"

  • Presenter: Ramamurti Shankar, Yale University
  • Host: Rahul Nandkishore
  • Abstract: In this talk I will describe the remarkable life and mathematics of Srinivasa Ramanujan (1887-1920), an unknown self-educated clerk from South India who stunned the world of western mathematics with his results on number theory, modular functions etc., that continue to challenge us till this day. I will describe his early life in India, his discovery by Cambridge mathematician G H Hardy, his few years in Cambridge and his untimely death at age 32.

September 28 — "Shared vibrations:  How photosynthetic light harvesting approaches 100% efficiency”

  • Presenter: David Jonas, Department of Chemistry and Biochemistry, University of Colorado Boulder
  • Host: John Price
  • Abstract: Almost all life on earth depends on photosynthesis, and almost all the power our civilization uses has been stored as fuel by photosynthesis.  In photosynthesis, light is harvested by antenna proteins that can transfer the photon’s energy to a reaction center with near unit quantum efficiency.  The remarkable efficiency of these energy transfer processes has been a mystery for over 60 years and we cannot replicate it artificially.  Recent femtosecond two-dimensional (2D) spectroscopy experiments on antenna proteins found signatures initially attributed to electronic coherence that have sparked discussion about the role of quantum mechanics in biology; it is puzzling that these signatures persist for longer than the apparent energy transfer timescale.   We have recently shown that intramolecular vibrations shared across pigments can drive electronic energy transfer outside the Born-Oppenheimer picture of fast electrons and slow vibrations.  Such shared vibrations on the ground electronic state of the antenna generate all of the observed 2D signatures and their properties reveal the design principle for the antenna.  There are indications that this new mechanism may be operative in a variety of antenna proteins using 5 different photosynthetic pigments that are responsible for over half of the light harvesting on our planet.

**Special Colloquium/Nuclear Particle Physics Seminar** Monday, October 3 — "The Physics of Non-Hydrodynamic Modes"

  • Presenter: Paul Romatschke, University of Colorado Boulder
  • NOTE SPECIAL LOCATION: DUAN G125
  • Abstract: Examples for hydrodynamic collective modes are sound waves, shear and diffusive modes. But what are non-hydrodynamic collective modes? Most physicists likely have never ever heard about non-hydrodynamic modes in their entire career. Indeed, there does not seem to be a single textbook on this topic. This colloquium will give an introduction to the physics of non-hydrodynamic modes, featuring gravitational waves, string theory predictions for experiment, the coolest and hottest stuff on earth and high-temperature superconductors.

October 5 — “A synthetic quantum magnet made of hundreds of trapped ions”

  • Presenter: John Bollinger, NIST Boulder
  • Host: Scott Diddams
  • Abstract: Entanglement between individual quantum objects exponentially increases the complexity of quantum many-body systems, so systems with more than 30-40 quantum bits cannot be fully studied using conventional techniques and computers. To make progress at this frontier of physics, Feynman’s pioneering ideas of quantum computation and quantum simulation are now being pursued in a wide variety of well-controlled quantum platforms.  Trapped-ions are naturally suited for simulating quantum magnetism, and exhibit desirable properties such as high-fidelity state preparation and readout, and long trapping and coherence times.  I will discuss how variable range, quantum magnetic interactions can be engineered with trapped ions, focusing on our work with 2-dimensional arrays of several hundred ions crystallized in a Penning ion trap.  In particular, I will highlight our recent experiments that benchmark quantum dynamics and entanglement, and utilize our ability to time-reverse the dynamics to measure out-of-time-order correlation functions that quantify the spread of quantum information throughout the system.

Graphic describing Compactifications - Quevedo ColloquiumOctober 12 — "On string theory, particle physics and cosmology"

  • Presenter: Fernando Quevedo, Director - ICTP, Trieste and Cambridge University
  • Host: Shanta de Alwis
  • Abstract: An overview will be given for the recent developments in string theoretical scenarios to address particle physics and cosmology questions.

October 19 — "From BEC to CEO: the Entrepreneurial Experience"

  • Presenter: Chris Myatt, CEO - MBio Diagnostics
  • Host: Scott Diddams
  • Abstract: Can academic training in physics – at CU, JILA, and at NIST – prepare you to start a company?  While the subject of your research may not be directly applicable to industrial problems—in my case, Bose-Einstein condensation and quantum computing—the skill sets and tools you develop are of great value in preparing you to start a company, or to find a job in industry.  I will discuss briefly the two companies I have founded, provide an overview of the technology of each, what it takes to get going, and the lessons learned in doing so.

October 26 — "Exploiting Disorder for Global and Local Response"

  • Presenter: Sidney Nagel, University of Chicago
  • Host: Noel Clark
  • Abstract: We are customarily taught to understand ordinary solids by considering perturbations about a periodic structure.  This approach becomes increasingly untenable as the amount of disorder in the solid increases.  In a crystal with only one atom per unit cell, all atoms play the same role in producing the solid's global response to external perturbations. Disordered materials are not similarly constrained and a new principle emerges: independence of bond-level response. This allows one to drive the system to different regimes of behavior by successively removing individual bonds. We can thus exploit disorder to achieve unique, varied, textured and tunable global response. We can use similar pruning techniques to achieve long-range interactions inspired by allosteric behavior in proteins. This allows a local input strain to control the local strain at a distant site in the network.

November 2 — "A Bridge Too Far: The Demise of the Superconducting Super Collider"

  • Presenter: Michael Riordan, Author
  • Host: Allan Franklin
  • Abstract: In October 1993 the US Congress terminated the Superconducting Super Collider — at over $10 billion the largest and costliest basic-science project ever attempted.  It was a disastrous loss for the nation’s high-energy physics community. With the 2012 discovery of the Higgs boson at CERN’s Large Hadron Collider, Europe has assumed world leadership in this field.
    A combination of fiscal austerity, continuing SSC cost overruns, intense Congressional scrutiny, lack of major foreign contributions, waning Presidential support, and the widespread public perception of mismanagement led to the project’s demise nearly five years after it had begun. Its termination occurred against the political backdrop of changing scientific needs as US science policy shifted to a post-Cold War footing during the early 1990s. And the growing cost of the SSC inevitably exerted undue pressure upon other worthy research, thus weakening its support in Congress and the broader scientific community.
    As underscored by the Higgs boson discovery, at a mass substantially below that of the top quark, the SSC did not need to collide protons at 40 TeV in order to attain its premier physics goal. The selection of this design energy was governed more by politics than by physics, given that Europeans could build the LHC by eventually installing superconducting magnets in the LEP tunnel under construction in the mid-1980s. In hindsight, there were good alternative projects the US high-energy physics community could have pursued that did not involve building a gargantuan, multibillion-dollar machine at a green-field site in Texas.

November 9 — "The physics of cell division"

  • Presenter: Meredith Betterton, University of Colorado Boulder
  • Host: John Price
  • Abstract: Cells are the basic unit of life. All life on earth depends on cells’ ability to duplicate themselves. In order to divide successfully, cells must solve fascinating physics problems, which this talk will introduce assuming no biology background. A key step in cell division is ensuring that each of the daughter cells inherits a single copy of the genetic material. In eukaryotes, a self-organized machine called the mitotic spindle exerts forces that physically move the chromosomes. This cellular machine is composed of microtubules, molecular motors, and associated molecules. We are using theory, simulation, and experiment to address fundamental physics questions related to mitosis, including how the mitotic spindle structure self assembles and achieves the correct size, how the spindle organizes and moves chromosomes, and how these same components outside of cells can create nonequilibrium materials that exhibit new physics.

John Martinis PortraitNovember 16 — "What’s next after Moore’s law: quantum computing"

  • Presenter: John Martinis, Google and UC Santa Barbara
  • Host: John Price
  • Abstract: As microelectronics technology nears the end of exponential growth over time, known as Moore’s law, there is a renewed interest in new computing paradigms such as quantum computing. After many years of fundamental research on superconducting quantum devices, I recently moved my research program to Google with the goal of building a useful quantum computer. Following Feynman’s vision, I will highlight a proof-of-principle experiment to simulate a chemical reaction that finds an interaction cross section. I will also outline a “quantum supremacy” experiment that will demonstrate the exponential power of a quantum processor by checking its output with a classical computer, which is intractable for even the world's most advanced classical supercomputer beyond 45-50 qubits. We are working to perform this experiment in the next year.
    John Martinis currently heads the quantum-hardware team at Google. John started the field of research on quantum devices as a graduate student at UC Berkeley in 1985, and has continued this research at NIST Boulder, UC Santa Barbara, and now Google. In 2010 he was awarded the AAAS science breakthrough of the year, and in 2014 was awarded the London Prize for low-temperature physics research.

November 23 — Fall Break; No Colloquium

November 30 — "Transport and Localization in many-body nuclear spin systems"

  • Presenter: Paola Cappellaro, Massachusetts Institute of Technology
  • Host: Ana Maria Rey
  • Abstract: A large-scale quantum computer could solve problems that would take classical computers longer than the age of the universe to crack, with profound implications for cryptography, chemistry, material science, and many areas of physics. However, to reach this goal we need to control large quantum systems, where the many-body dynamics becomes often fragile and very complex.
    Among the many questions and challenges that arise when working toward this goal, I will address two questions in my talk: How can we transfer quantum information from one quantum register to another?
    How can we preserve quantum information in the presence of strong interactions?
    Using a nuclear spin chain as an exemplary experimental system, and the tools of Hamiltonian engineering, I will show how spin chains can act as quantum wires in a distributed quantum computing architecture, transporting information and entanglement. I will then show how disorder can quench the transport of information, a phenomenon known as localization. This phenomenon might actually be a feature in some situations, as it allows preserving local quantum information for later retrieval and prevents thermalization. Is localization however possible even in the presence of long-range interaction? I will show experimental signatures that a logarithmic growth of long-range correlation is still present in interacting systems, a sign of many-body localization.

**Special Colloquium: Monday, December 5 at 4:00 p.m.** — "Symmetry, Topology and Bacteria"

  • Smalyukh GraphicNOTE SPECIAL LOCATION: DUAN G125
  • Presenter: Ivan Smalyukh, University of Colorado Boulder
  • Abstract: Einstein introduced the “colloidal atom” paradigm, but only high-symmetry colloidal crystals could be realized within a century or so. Born developed a theory of polar ordered fluids, but only nonpolar ones could be observed. Heisenberg proposed 3D solitons as models of particles in continuous fields, but Derrick put forward a theorem that they cannot be stable. I will discuss how, addressing these long-standing challenges, we realize the lowest symmetry triclinic colloidal crystals [1] and biaxial ferromagnetic fluids [2], as well as the static 3D topological solitons within them [3]. With production aided by bacteria, such unusual materials promise a solution to the window inefficiency problem and other technological uses.
    1. H. Mundoor, B. Senyuk & I.I. Smalyukh. Science 352, 69 (2016).
    2. Q. Liu, P.J. Ackerman, T.C. Lubensky & I.I. Smalyukh. PNAS 113, 10479 (2016).
    3. P.J. Ackerman & I.I. Smalyukh. Nature Mater. DOI:10.1038/NMAT4826 (2016).

For more information about colloquia this semester, contact: John Price.

Colloquia are Wednesdays at 4:00 p.m. in DUAN G1B20, unless otherwise noted.

Coffee, tea and cookies will be available before regular colloquia beginning at 3:45 p.m. in DUAN G1B31.

January 13 — "Looking for Dark Matter with Atomic Clocks and Gravitational Wave Detectors"

  • Presenter: Asimina Arvanitaki, Perimeter Institute
  • Host: Shanta de Alwis
  • Abstract: When we think about Particle physics the first thing that comes to mind is colliders and high energies. In this talk, I will describe how low energy experiments can probe new phenomena, new particles and new forces of nature. I will demonstrate this through two seemingly different experiments that test the same aspects of Dark Matter.  In String Theory, fundamental constants, such as the electron mass or charge, are determined by fields known as moduli. When these fields are the Dark Matter of our Universe, they will cause the fundamental constants to oscillate locally with a frequency set by the Dark Matter mass. For frequencies smaller than 1 Hz atomic clocks can easily pick up these oscillations with their immense sensitivity. For higher frequencies above 1 kHz, Dark Matter can excite acoustic modes in resonant mass detectors originally designed to detect gravitational radiation from astrophysical sources. Both techniques can extend searches for this type of Dark Matter by several order of magnitude in the near future.

January 20 — "From atoms to brains: Microfabricated atomic sensors for non-invasive magnetic brain imaging?"

  • Presenter: Svenja Knappe, NIST Boulder
  • Host: Markus Raschke
  • Abstract: Laser spectroscopy of atoms can be used as a sensitive tool to measure many physical properties such as time, length, acceleration, and temperature. It has also been used to measure magnetic fields as precisely as the best superconducting magnetometers currently available. Our group has been trying to miniaturize these atom-based magnetic field sensors by use of microfabrication technologies. We have developed a non-invasive multichannel magnetic imaging system sensitive enough to detect the tiny magnetic fields emitted by the brain. These uncooled small sensors could open new and exciting possibilities for brain imaging. They could improve the spatial resolution of the images, open the door for imaging during real-world scenarios, long-term telemetry, and maybe even enable wearable systems in the future.

January 27 — "Simulating QCD at non-zero matter density"

  • Presenter: Philippe de Forcrand, ETH Zurich and CERN
  • Host: Paul Romatschke
  • Abstract: The study of the properties of Quantum Chromodynamics by Monte Carlo simulations, called Lattice QCD, has been highly successful in the regime where matter and anti-matter densities are equal. When they are not, the notorious "sign problem" occurs, and standard Monte Carlo sampling cannot be applied.
    I review the nature of the "sign problem", the importance of addressing it, and offer some views on current efforts to circumvent it.

RESCHEDULED Thursday, January 28 — SPECIAL Physics Colloquium "Studying the Dark Side of the Nucleus:  From Neutron Skins to Neutron Stars"

  • Presenter: Seamus Riordan, Stony Brook University
  • Host: Jamie Nagle
  • NOTE SPECIAL LOCATION: DUAN G130
  • Abstract: The neutron densities in atomic nuclei are notoriously difficult to observe with high precision: the standard tool of electromagnetic interactions which has been used to map out the nuclear charge distributions simply doesn't see them. In fact, it has only recently been experimentally confirmed that the neutron-rich lead nucleus even has a neutron skin, and is only a fraction of a neutron radius thick. Encoded in these distributions is a wealth of important information about how the strong nuclear force builds systems where the number of protons and neutrons are unequal. This information has bearing not only for our understanding of asymmetric nuclei, but also in the construction of extreme systems like neutron stars. Fortunately, nature gives us a novel way to image this side of the nucleus: through fundamental weak force interactions, which interact primarily to neutrons rather than protons. In this colloquium I will discuss why these neutron distributions play an important part in our understanding of nuclear physics and astrophysics, how one images such tiny systems with electron beams, and the recent and upcoming experimental efforts for such measurements.

Monday, February 1 — SPECIAL Physics Colloquium "High-Energy-Density Physics: Laser-driven Fusion to Fundamental Plasma Science"

  • Presenter: Mario Manuel, Smithsonian Astrophysical Society
  • Host: Tobin Munsat
  • NOTE SPECIAL LOCATION: DUAN G130
  • Abstract: Inertial confinement fusion (ICF) is a major research effort underway in the US and abroad to achieve net energy production through nuclear fusion of hydrogen isotopes. Rather than using externally applied magnetic fields, as in magnetic confinement fusion (e.g. as in a tokamak), ICF utilizes spherical capsules of deuterium-tritium fuel. These capsules are compressed through the use of high-power lasers to produce fuel temperatures and densities higher than those in the center of the sun. The fuel is arranged in such a way as to create a runaway thermal instability for the short period that the fuel is held together by its own inertia. In this talk, I will briefly describe the general ICF concept and the facilities where this research takes place.
    Laser facilities used to study ICF also provide unique opportunities to study fundamental plasma science in the high-energy-density regime, i.e. systems with pressures >1 Mbar. One of the great challenges to the ICF program is understanding how the Rayleigh-Taylor (RT) instability behaves in the HED system produced by the interaction of intense lasers with matter. This classical hydrodynamic instability also occurs in laser-driven plasma systems where the acceleration direction opposes the density gradient. One complexity involved with RT in these systems is the generation of magnetic fields due the the Biermann battery mechanism. Creation of RT-induced magnetic fields in HED plasmas will be thoroughly discussed and I will describe our experimental results that first demonstrated their existence 30+ years after the theoretical predictions.

February 3 — "The Water Surface: Complex, Dynamic and Wet"

  • Presenter: Mischa Bonn, Max-Planck-Institute for Polymer Sciences, Mainz
  • Host: Markus Raschke
  • Abstract: Water surfaces and interfaces are ubiquitous, not just in nature (e.g. at the boundaries of cells, in rain drops, oceans, rivers and lakes) but also in many technological applications (such as electrochemistry and photocatalytic water splitting). Water is a rather unique liquid, owing to its strong intermolecular interactions: strong hydrogen bonds hold water molecules together. At the surface of water, the water hydrogen-bonded network is abruptly interrupted, conferring properties on interfacial water different from bulk water [1].
    We elucidate the structure and structural dynamics of interfacial water using surface-specific vibrational spectroscopy of interfacial water molecules, with femtosecond time resolution. Specifically, we find that the interface is structurally more heterogeneous [2,3] and substantially more dynamical [4] than bulk water. We reveal the nature of the heterogeneity, and quantify the reorientational dynamics of specifically interfacial water molecules. Finally, we show that the evaporation of water – i.e. the release of individual water molecules from the bulk into the gas phase – is not a purely stochastic event. Rather, the evaporation follows one specific pathway, involving a delicately timed, concerted motion of several water molecules to ‘launch’ a single molecule from the surface [5].
    References
    [1] Bonn, M.; Nagata, Y.; Backus, E.H.G.; Angew. Chem.-Intern. Ed. 2015, 54, 5560.
    [2] Hsieh, C.S.; Okuno, M.; Backus, E. H. G.; Hunger, J.; Nagata, Y.; Bonn, M.. Angew. Chem.-Intern. Ed. 2014, 31, 8146 (VIP paper).
    [3] van der Post, S. T.; Hsieh, C.-S.; Okuno, M.; Nagata, Y.; Bakker, H. J.; Bonn, M.; Hunger, J. Nat. Commun. 2015, 6, 8384.
    [4] Hsieh, C. S.; Campen, R. K.; M. Okuno; E. H. G. Backus; Y. Nagata; and M. Bonn, Proc. Nat. Acad. Sci. USA 2013, 110, 18780.
    [5] Nagata, Y.; Usui, K.; Bonn, M., Phys. Rev. Lett. 2015, 115, 236102.

February 10 — "Atomic physics meets nanophotonics: creating complex quantum states of matter and light"

  • Presenter: Darrick Chang, Institute of Photonic Sciences
  • Host: Markus Raschke
  • Abstract: Significant efforts have been made to interface cold atoms with micro- and nano-photonic systems in recent years. Originally, it was envisioned that the migration to these systems from free-space atomic ensemble or macroscopic cavity QED experiments could dramatically improve figures of merit and facilitate scalability for applications such as quantum information processing. However, a more interesting scenario would be if nanophotonic systems could yield new paradigms for controlling quantum light-matter interactions, which have no obvious counterpart in macroscopic settings.
    Here, we describe one paradigm for novel physics, based upon the coupling of atoms to photonic crystal structures. In particular, we show that atoms can become dressed by localized photonic "clouds" of tunable size. This cloud behaves much like an external cavity, but which is attached to the position of the atom. This dynamically induced cavity can then mediate long-range spin interactions or forces between atoms, yielding an exotic quantum material where spins, phonons, and photons are strongly coupled.

Thursday, February 11 — SPECIAL Physics Colloquium "Imaging the Physics of Magnetically Confined Fusion"

  • Presenter: Dr. Benjamin Tobias, Princeton Plasma Physics Laboratory
  • Host: Tobin Munsat
  • NOTE SPECIAL TIME AND LOCATION: 2:00 p.m. DUAN F1117 (Commons Room)
  • Abstract: Electron Cyclotron Emission Imaging (ECEI) and Microwave Imaging Reflectometry (MIR) are powerful visualization tools that are purpose built for tokamak research, and they have become integral to experiments at the cutting edge of fusion science. They provide unique data that was simply not available to previous generations of scientists and bring us closer than ever to understanding and controlling instabilities. 2D and 3D images of the core plasma help to validate modeling of Alfvénic oscillations that can limit plasma self-heating in a burning reactor by diagnosing their interaction with energetic ions. Images of the edge plasma help to explain how and why transients occur, and what techniques can excite benign modes to regulate the stability of this region. To address the most dangerous eventuality, a rapid and violent disruption of plasma confinement, we apply these tools in the study of helical modes that tear the internal magnetic surfaces. The vast majority of tokamak disruptions are attributed to these tearing modes, and using microwave imaging data we are able to validate magnetohydrodynamic (MHD) modeling, quantify the forces omitted by single fluid resistive theory, and accurately prescribe inputs to more sophisticated analysis that can help us understand the successes and failures of disruption avoidance and mitigation techniques.

Monday, February 15 — SPECIAL Physics Colloquium "Probing the quark–gluon plasma with light-flavor hadrons with the ALICE detector at the LHC"

  • Presenter: Michele Floris, CERN
  • Host: Jamie Nagle
  • NOTE SPECIAL LOCATION: DUAN G125
  • Abstract: Quantum ChromoDynamics (QCD) describes the interaction between the elementary constituents of hadronic matter, the quarks and gluons. Quarks and gluons are not observed as free particles, but are confined inside color-singlet hadrons. QCD, however, predicts the existence of a phase of matter at high temperature (T > 10^12 K) where quarks and gluons are no longer confined, called the Quark–Gluon Plasma (QGP). The QGP can be created and studied in the laboratory colliding heavy nuclei at ultra-relativistic energies. The ALICE experiment at the CERN LHC is pursuing this program at the energy frontier (\sqrt{s_NN} > 2.76 TeV).

    After a brief introduction on the physics of confinement and heavy-ion experiments, I will discuss recent results from the ALICE experiment on the collective properties and hadronization mechanism of the system created in the collision. Measurements of light-flavor hadrons obtained in lead–lead, proton–proton and proton–lead collisions will be compared and contrasted. These studies revealed unexpected features, which are currently not clarified and could lead to a better understanding of high-energy hadronic interactions.

February 17— "Investigative Science Learning Environment: Turning our students into collaborative participants in the practice of physics"  

  • Presenter: Eugenia Etkina, Rutgers University
  • Host: Noah Finkelstein
  • Abstract: Scientists and especially physicists have their own, unique ways of developing new knowledge, solving new problems, and communicating about what they do. These form a set of cultural norms and practices that we call “physics.” Can students become enculturated into physics in a one year introductory course, or does “doing physics” remain the exclusive purview of professionals who have acquired their skills through years of training? Development of the Next Generation Science Standards, revisions to AP courses, and a new MCAT suggest that these aspects of physics (and other sciences) are as valuable as the final product of scientific labor—concepts and mathematical representations—that traditionally have been the sole focus of science courses. Science practices are the central elements of all these innovations. In my talk I will describe Investigative Science Learning environment - an instructional philosophy that allows us to make these practices a centerpiece of learning physics without losing conceptual and mathematical focus. I will also discuss ways to assess these complex practices.

Thursday, February 18 — SPECIAL Physics Colloquium "Nature's Keys: Two of the Fundamental Plasma Processes that Unlock our World"

  • Presenter: Seth Dorfman, UCLA
  • Host: Tobin Munsat
  • NOTE SPECIAL LOCATION: DUAN F1117 - Commons Room
  • NOTE SPECIAL TIME: 2:00 p.m.
  • Abstract: Plasma makes up 99.9% of the visible matter in the universe and is crucial to building a working fusion power plant, but many fundamental processes that occur in space and laboratory plasmas remain poorly understood. Interesting unsolved problems abound: Why is the outer layer of the sun (the solar corona) much hotter than the photosphere below, when from adiabatic considerations we would expect the reverse? How can we reduce losses to improve the performance of fusion plasmas? What determines the evolution of space weather that can damage our sensitive infrastructure? I will discuss fundamental plasma physics as the key to solving these and other problems, focusing on two examples: magnetic reconnection and non-linear physics of Alfvén waves.

    Magnetic reconnection is an important energy release mechanism to consider in contexts such as eruptions on the sun and loss of plasma in experimental fusion devices. In both cases, a slow build up phase is followed by a quick release of magnetic energy, but this impulsive behavior is not fully understood. I will show results from a dedicated laboratory experiment at Princeton University in which 3-D physics is necessary to explain the observed impulsive events. The experiments have key features in common with space observations that will inform future comparative studies.

    Alfvén waves are fundamental modes of a plasma with a magnetic field. The non-linear behavior of these waves may be key in contexts such as space weather and the scattering and loss of energetic particles in fusion devices. One important non-linear process with a long history of theoretical and simulation studies is a class of parametric instabilities in which a large amplitude Alfvén wave produces various daughter modes. I will show results from recent experiments at the Large Plasma Device at UCLA which represent the first observation of this type of instability in the laboratory.

Monday, February 22 — SPECIAL Physics Colloquium "Jet and photon probes of hot, dense nuclear matter at the Large Hadron Collider"

  • Presenter: Dennis Perepelitsa, Brookhaven National Laboratory
  • Host: Jamie Nagle
  • NOTE SPECIAL LOCATION: DUAN G125
  • Abstract: When large nuclei are accelerated to relativistic energies and brought into collision at the CERN Large Hadron Collider (LHC), the enormous temperature and energy density in the nuclear system trigger a phase transition into an exotic form of matter. The resulting quark-gluon plasma (QGP) evolves in an expanding, flowing fireball, and investigating its remarkable properties allows us to study how the theory of the strong nuclear force (quantum chromodynamics, or QCD) manifests itself in a novel high-density, high-temperature regime. Since the first nucleus-nucleus collisions in late 2010, a rich experimental program with the large, state-of-the-art detectors at the LHC has flourished. In this talk, I will focus on two valuable experimental tools developed to explore the QGP: reconstructed jets which arise from cascades of strongly-interacting quarks and gluons passing through the plasma; and high-energy photons which escape the interaction zone without further interaction.

February 24 — "Chaos and Thermalization in Many-Body Quantum Systems"

  • Presenter: Mark Srednicki, University of California, Santa Barbara
  • Host: Paul Beale
  • Abstract: The question of how isolated systems come to thermal equilibrium has been debated for more than a century. I will present a simple picture of how thermalization of many-body systems can occur, with universal properties of chaotic quantum dynamics as the underlying mechanism. A large array of analytic, numerical, and experimental evidence now supports this picture in many cases.

Thursday, February 25 — SPECIAL Physics Colloquium, "Plasma Wakefield Acceleration: Surfing on a Wave of Plasma"

  • Presenter: Michael Litos, SLAC National Accelerator Laboratory
  • Host: Tobin Munsat
  • NOTE SPECIAL LOCATION: DUAN G126
  • NOTE SPECIAL TIME: 2:00 p.m.
  • Abstract: The passage of an intense laser pulse or particle beam through a cold plasma can set up an oscillation in the plasma electrons with properties that are attractive for the acceleration of particle beams in a scheme known as plasma wakefield acceleration. These relativistic plasma waves can sustain incredibly high longitudinal electric fields traveling with a phase velocity near the speed of light. By pushing the plasma harder with a more intense driver pulse, non-linear responses may be evoked with yet more interesting properties. One of the greatest challenges in the field right now is the ability to form, control, and diagnose the plasma source with a sufficiently high resolution to better understand and manipulate the beam-plasma interaction. This line of research offers great promise for the creation of compact, inexpensive particle accelerators that may be used in applications ranging from high energy colliders to X-ray free electron lasers that can fit in a university lab. It also serves as an interesting example of how the proper combination of plasmas, lasers, and particle beams can lead to a sum that is greater than its parts.

Monday, February 29 — SPECIAL Physics Colloquium, "Jet Quenching in Heavy-Ion Collisions : Probing the Perfect Liquid"

  • Presenter: Aaron Angerami, Columbia University
  • Host: Jamie Nagle
  • NOTE SPECIAL LOCATION: DUAN G125
  • Abstract: Relativistic heavy-ion collisions produce matter at the highest temperatures accessible in the laboratory. Results from the RHIC experiments show that the system produced in these collisions behaves like a near-perfect fluid. These observations indicate that strong-coupling dynamics dominate the long wavelength behavior of the system and are in surprising contrast to initial expectations that system would form a weakly-coupled plasma. This exciting discovery has led to a number of questions about the nature of strongly coupled quantum systems and how such behavior can emerge from a theory possessing asymptotic freedom. Another discovery of the RHIC program was the observation of jet quenching, where energetic partons produced in the early stages of the collisions lose energy though their interactions with the medium. Jets probe the medium at a variety of length scales and are thus sensitive to both its microscopic structure and the onset of the strong coupling. In this colloquium I will present the latest LHC jet measurements performed with the ATLAS experiment, in which precision techniques developed in high energy physics have been adapted to the heavy-ion environment. I will discuss the rapidly improving theoretical picture of jet quenching, the implications of new measurement capabilities during the next lead ion runs at the LHC, and the role of a future detector to measure jets at RHIC. 

March 2 — "The Search for 100 Earths"

  • Presenter: Debra Fischer, Yale University
  • Host: Scott Diddams
  • Abstract: Exoplanets are an important subfield of astronomy and there has been an impressive rate of discovery over the past two decades. Hundreds of exoplanets have been detected using the Doppler technique and the NASA Kepler mission discovered thousands of transiting planets, providing important statistical information about the size and ubiquity of other worlds. However, the vast majority of planets around nearby stars have escaped detection; a radial velocity precision of about 10 cm/s is required to discover potentially habitable worlds and to unravel complex multi-planet architectures. Such high precision would also dramatically improve the efficiency of space-based transit missions by providing the masses needed to estimate bulk densities and model the internal structure of exoplanets. The future of exoplanet science has very different trajectories depending on the precision that can ultimately be achieved with Doppler measurements.
    I will describe the work my team is carrying out to reach 10 cm/s precision with the radial velocity technique. We are commissioning a new instrument, the EXPRES spectrograph, at the Discovery Channel Telescope to carry out a search for 100 Earths in 2017.

Monday, March 7 — SPECIAL Physics Colloquium, "Probing Hot Nuclear Matter with Heavy Quarks at the Relativistic Heavy Ion Collider"

  • Presenter: Darren McGlinchey, University of Colorado
  • Host: Jamie Nagle
  • NOTE SPECIAL LOCATION: DUAN G125
  • Abstract: High energy heavy ion collisions, like those performed at the Relativistic Heavy Ion Collider (RHIC), allow us to test our understanding of nuclear physics at the highest temperatures accessible in the laboratory. At these high temperatures, a new phase of nuclear matter called the Quark Gluon Plasma (QGP), where the fundamental quarks and gluons are no longer confined within hadrons, is created. The RHIC experiments discovered that the QGP is strongly coupled and behaves as a nearly perfect fluid, contrary to initial expectations. Understanding the microscopic structure of the QGP, and its strongly coupled nature, requires calibrated probes at varying length scales. Heavy quarks, namely charm and bottom, are produced in initial hard scatterings, and therefore provide an excellent tool for these studies as they experience the full evolution of the produced medium. In this colloquium, I will discuss the use of heavy quarks as a probe of the medium produced in heavy ion collisions including recent experimental advances made possible by detector upgrades of the PHENIX experiment at RHIC.

March 9 — "Quantum simulations: from condensed matter to high energy models"

  • Presenter: Ignacio Cirac, Max Planck Institute of Quantum Optics
  • Host: Murray Holland
  • Abstract: Many-body quantum systems are very hard to describe and simulate in general, since the dimension of the state space grows exponentially with the number of particles, volume, etc. Cold atoms in optical lattices as well as trapped ions may help us in that task, as one can engineer the interactions among the atoms in order to emulate many-body quantum problems. In this talk I will briefly summarize proposals to simulate condensed matter as well as high energy physics models with those systems. I will also show how photonic crystal structures can be used to design subwavelength optical lattices in two dimensions for ultracold atoms, potentially achieving a better performance than current experimental set-ups.

Monday, March 14 — SPECIAL Physics Colloquium, "Testing the fundamental nature of neutrinos with double beta decay"

  • Presenter: Dr. David Moore, Stanford University
  • Host: Jamie Nagle
  • NOTE SPECIAL LOCATION: DUAN G125
  • Abstract: The discovery of neutrino oscillations has demonstrated that neutrinos have small, but non-zero masses. These masses are at least 10^6 times smaller than those of the other fundamental particles, suggesting that neutrinos could be getting their masses through a different physical mechanism. Understanding the fundamental nature of neutrinos and the mechanism by which they acquire mass are key goals of nuclear and particle physics in the coming years.
    In this talk I will describe current and future searches for neutrinoless double beta decay with the Enriched Xenon Observatory (EXO). This extremely rare nuclear decay can occur if neutrinos are Majorana particles, i.e. if neutrinos and anti-neutrinos are identical. Searches for this lepton number violating decay will probe extensions to the Standard Model that attempt to account for the mechanism by which neutrinos acquire mass and could constrain the absolute neutrino mass scale. I will discuss the current status of the EXO experimental program and plans for next-generation detectors, which have substantial possibility to observe this beyond the Standard Model process.

March 16 — "Lessons of the warm Pliocene – Melding knowledge from geology and physics"

  • Presenter: Bette Otto-Bliesner, NCAR
  • Host: Scott Diddams
  • Abstract: Studying past geologic warm periods can give valuable insight into important processes that may operate in the climate system during a warm regime. It also allows testing of our climate models ‘out-of-sample’. That is, climate models are most often developed and tested for the period of instrumental measurements, before being used to project the future. But the likely future long-term consequences of anthropogenic greenhouse gas changes is outside the range of this testing. 

    The mid-Pliocene warm period (~ 3 million years ago) has been considered a possible analog for the future. Atmospheric carbon dioxide concentrations for this period have been estimated to be approximately 350 to 450 ppmv. We have now nearly surpassed globally the mid-point of this range and could surpass 450 ppmv by shortly after year 2030 in the most dire pathway of future emissions. In this talk, I will review the geological reconstructions for the mid-Pliocene that indicate strong warming at polar latitudes and much higher sea level than today, and the various hypotheses that have been proposed to explain this warmth. These mechanisms and feedbacks are tested with climate models that simulate the responses of the atmosphere, ocean, sea ice, and land to the greenhouse gas forcing. I will conclude with a discussion of the possible reasons for the mismatches between the data and models.

March 23 - Spring Break; No Colloquium

March 30 — "New Findings in Materials in Extreme Environments"

  • Presenter: Russel Hemley, Geophysical Laboratory, Carnegie Institution of Washington
  • Host: Markus Raschke and Mike Ritzwoller
  • Abstract: Extreme environments, and in particular high pressures and temperatures, produce profound effects on condensed matter and materials -- from structure, bonding, and chemical reactivity to bulk transport properties. It is now possibly to generate multimegabar pressures (e.g., >300 GPa) and temperatures from millikelvins to thousands of degrees in the laboratory under static conditions. A broad range of novel phenomena and materials are being observed, including unusual transitions between insulating and metallic phases, new superconductors and ferroelectrics, and novel structural and superhard materials.  Of particular interest have been pressure-induced transitions in simple elemental and molecular systems such as hydrogen. Altogether, these studies have implications for problems in physics and chemistry, planetary science, geoscience, astrophysics, and even soft matter and biology, and the new materials being discovered may find potential applications in energy and other technologies. In this effort, large experimental facilities such as accelerator-based x-ray, neutron scattering, and large laser sources are allowing new types of measurements to be made as well as still more extreme environments to be reached in the laboratory. 

April 6 — "Twisting the quantum"

  • Presenter: Charles Clark, National Institute of Standards and Technology and the University of Maryland
  • Host: Judah Levine
  • Abstract: Wave motions in nature were known to the ancients, and their mathematical expression in physics today is essentially the same as that first provided by d'Alembert and Euler in the mid-18th century. Yet it was only in 1992 that physicists managed to control a basic property of light waves: their capability of swirling around their own axis of propagation. During the past decade such techniques of control have also been developed for quantum particles: atoms, electrons and neutrons.

    I will present a simple description of these phenomena, emphasizing the most basic aspects of wave and quantum particle motion, and showing how these are used in our recent work on twisting neutron wavefunctions [1].

    1. “Controlling Neutron Orbital Angular Momentum,” C. W. Clark, R. Barankov, M. G. Huber, M. Arif, D. G. Cory and D. A. Pushin, Nature 525, 504 (2015)

April 13 — "How old are Saturn’s rings, what is going on within Saturn’s moon Enceladus, and how dust measurements help to answer these questions"

  • Presenter: Sascha Kempf, University of Colorado Boulder, LASP
  • Host: Anna Hasenfratz
  • Abstract: Even 450 years after Galileo Galilei’s discovery of Saturn’s rings, their origin and evolution is still not known. The rings are the brightest of the four ring systems in the solar system and have at least the mass of the moon Mimas. Interactions with Saturn’s moons and viscous spreading of the ring material seem to imply a ring age of about a tenth of the age of the Saturnian system. A young ring age is problematic because the disruption of a Mimas-sized body or a comet in the Roche zone of Saturn would result in a ring with a much larger rock content than observed today. The unique ring color resulting mainly from the pollution of the ring material with interplanetary meteoroids provides a key for constraining the ring age. Direct measurements of the meteoroid flux into the Saturnian system by Cassini’s Cosmic Dust Analyzer (CDA) allowed us for the first time to constrain the ring age.

    The discovery that Saturn’s small ice moon Enceladus maintains an active ice volcano is surely one of the most exiting findings by the Cassini mission and data obtained by the Cosmic Dust Analyzer contributed significantly to our understanding of this phenomenon. In fact, knowledge of the dynamics and composition of the ice particles forming the plume allow us to obtain information about the moon’s interior and in particular provide evidence for a subsurface ocean. In October 2015 Cassini performed its last close flyby at Enceladus. Data obtained during this flyby together with numerical simulations allow us to constrain the Enceladus dust source rate and to draw conclusions about the emission of plume particles along the fractures in the south polar terrain.

April 20 - "Dipolar quantum gases of strongly magnetic Erbium atoms"

  • Presenter: Francesca Ferlaino, University of Innsbruck 
  • Host: Ana Maria Rey and Debbie Jin
  • Abstract: Given their strong magnetic moment and exotic electronic configuration, lanthanide atomic species disclose a plethora of intriguing phenomena in ultracold quantum physics. The large magnetic moment of these atoms reflects on a strong interparticle dipole-dipole interaction, which has both a long-range nature and an isotropic character. Here, we report on our latest results on quantum many-body and few-body physics based on a strongly-magnetic lanthanide, erbium (Er). Particular emphasis will be given to the dipolar Fermi gas and to the scattering properties of bosonic and fermionic Er, in which unconventional and fascinating phenomena appear as a result of both the magnetic and the orbital anisotropy of the underlying the native interactions between atoms.

Wednesday, April 27 — SPECIAL Physics Colloquium, "Ultrafast laser-driven processes in magnetic materials: A theoretical perspective"

  • Presenter: Peter Oppeneer, Dept. of Physics and Astronomy, Uppsala University, Uppsala, Sweden
  • Host: Margaret Murnane
  • NOTE SPECIAL LOCATION: JILA X317
  • NOTE SPECIAL TIME: 11:00 a.m.
  • Abstract: Through excitation of materials with ultrashort laser pulses it might be possible to reach novel, transient states of matter that cannot be reached under equilibrium conditions. One prominent example is that of ultrafast laser-induced demagnetization which was discovered 20 years ago. Femtosecond laser excitation of a ferromagnetic transition metal was found to cause an ultrafast magnetization quenching within about 300 fs, much faster than the equilibrium spin-lattice relaxation time. The origin of the unexpectedly fast demagnetization is not understood and is currently a topic of intense debates. In this talk I will give a survey of recent theories and discuss in more detail the electron-phonon spin-flip scattering and the superdiffusive transport models, in connection to insightful measurements that help to bring the problem’s solution closer. I will provide an outlook on future ultrafast magnetic processes, including all-optical magnetization reversal and laser-imparted magnetization.

April 27 — "Trillion Degree Matter"

  • Presenter: Gunther Roland, MIT 
  • Host: Paul Romatschke
  • Abstract: Experiments at large particle colliders like RHIC at Brookhaven Lab and LHC at CERN have used collisions of heavy nuclei to study a simple question:
    What are the properties of matter at extremely high temperature, in excess of several trillion Kelvin? At such temperatures, matter exists in the form of a plasma of quarks and gluons resembling the universe shortly after the Big Bang. We have found that the produced state of matter exhibits fascinating and somewhat surprising properties: Although its density exceeds that of water by 16 orders of magnitude, the quark-gluon plasma behaves like a near-perfect liquid. I will review the most striking experimental observations and describe new experiments aimed at elucidating the emergence of the plasma's unusual properties.

For more information about colloquia this semester, contact: Markus Raschke.

Colloquia are Wednesdays at 4:00 p.m. in DUAN G1B20, unless otherwise noted.

Coffee, tea and cookies will be available before regular colloquia beginning at 3:45 p.m. in DUAN G1B31.

August 26 — "The New Horizons Mission to Pluto: First Results"

  • Presenter: Mihaly Horanyi, LASP, University of Colorado Boulder
  • Host: Markus Raschke
  • Abstract: New Horizons, the fastest spacecraft ever, reached Pluto on July 14, 2015, following a close to a decade-long journey.  It gathered high-resolution images, spectral data, plasma and dust measurements. The small fraction of the data that has been downloaded to date already prompted the need to revise our understanding about the outer most regions of our solar system. Contrary to our expectations, Pluto turned out to be geologically active, and shows an exceptionally wide variety of terrain, including possibly Rocky Mountain sized ice glaciers. The talk will discuss the scientific motivation for the mission, its instruments, and some of the preliminary results. One of the seven instruments onboard New Horizons is the Student Dust Counter that was designed, built, and operated by generations of students at the University of Colorado, many of them from our Department of Physics.

September 2 — "Advocating Science"

  • Presenter: Rush Holt, C.E.O., American Association for the Advancement of Science (AAAS)
  • Host: Tobin Munsat
  • Abstract: Among the various ways of thinking and knowing about the universe and ourselves, science is special. Asking questions that can be answered empirically and engaging in open communication so that others can collectively review and verify possible answers lead to the most reliable knowledge—a knowledge that is powerfully applicable in daily life. Science is, as physician and essayist Lewis Thomas wrote, the “shrewdest maneuver” for discovering the world. This grand and clever enterprise, while surely not removing all worldly woes, brings beauty, wonderfully fulfilling intellectual pleasure, and cultural enrichment. It can lead to improved human interaction, more constructive commerce, and a better quality of life. Science helps bring what is a deep human need—a sense of progress. That progress is not assured, however. To thrive, science needs the support of the society it serves, and that support must be cultivated.

September 9 — "Water Storage in Planetary Interiors: Hydrogen Incorporation in High Pressure Minerals"

  • Presenter: Joe Smyth, University of Colorado Boulder
  • Host: Michael Ritzwoller
  • Abstract: Although Earth is a water planet, and water dominates all of the surface processes, the oceans are only 0.023 % of the planet’s mass (230 ppm). Hydrogen is soluble, to greater or lesser extent, in all of the oxygen minerals of the interior. The Earth’s mantle is solid rock composed of oxygen minerals, mostly silicates, and composes two thirds of the mass of the planet.  Small amounts of H incorporated in these minerals are thus a much larger potential reservoir of water than is the ocean. Hydrogen has a unique geochemistry and usually occurs as a hydroxyl (OH) group in minerals. Its substitution in nominally anhydrous silicates is typically charge-balanced by vacancy at a divalent metal site, which reduces the density of the crystal and increases the compressibility. Hydrogen is relatively mobile in these crystals and can facilitate deformation and increase electrical conductivity. By controlling deformation, H controls viscosity and thus convection. H substitution in these minerals can decrease P-wave and S-wave seismic velocities, as well as density, and lower the temperature onset of melting by hundreds of degrees C.  ‘Water’, incorporated in minerals, may thus control many of the processes of the interior that drive plate tectonics as well the surface processes.

September 16 — "Changing his Mind at the Speed of Thought: Einstein's Failed Attempts to Undiscover Gravitational Waves"

  • Presenter: Daniel Kennefick, University of Arkansas
  • Host: Markus Raschke and Allan Franklin
  • Abstract:  100 years ago, in November 1915, Einstein published his theory of General Relativity. This talk examines Einstein's life over the next several years, a period of war, poor health and personal turmoil, which ended with him becoming world famous in 1919 as a result of the famous British eclipse expedition which vindicated his theory. We also examine one important physics prediction which he deduced from the theory, that of gravitational waves. Here too, the path was far from smooth, and Einstein remained, for many years, very skeptical of their existence. This culminated in 1936 when he angrily withdraw a paper from the Physical Review after being criticized for trying to prove that his theory did not, after all, predict their existence.
  • Daniel Kennefick is a native of Ireland who earned his Ph.D. at Caltech working under a leading General Relativist, Kip Thorne. His fields of interest are gravitational waves, black holes and galactic structure. he is also a historian of gravitational physics and astronomy. He is a fellow of the American Physical Society. He has written a book on the history of gravitational waves and helps to edit the Collected Papers of Albert Einstein. He is a co-author of "An Einstein Encyclopaedia" to appear next month from Princeton University Press.

**Special Seminar** Thursday, September 17 — "Evidence in favor of the density wave wave theory of galactic spiral arms"

  • Presenter: Daniel Kennefick, University of Arkansas
  • Location: JILA Auditorium
  • Abstract: Since the work of Lin and Shu in the 1960s the density wave theory, in several different forms, has been the leading candidate for a theory explaining the ubiquitous spiral arm patters seen in disk galaxies. Other theories exist, and rival versions of the density wave theory exist, but there has been little success in using observations to decide which theories are more successful. We present three such observational tests which we have been working on recently. Firstly we present a relationship between spiral arm pitch angle (which measures how tightly wound a spiral arm is), central bulge mass and gas density in the disk of a galaxy. Such a relationship is predicted by the original density wave theory of Lin and Shu. Secondly we show that spiral arm pitch angle varies between measurements made in optical versus infrared images in a way which is predicted by the density wave theory. Thirdly we examine the extent to which the number of arms in a spiral pattern varies with disk density, a prediction made by the swing amplification version of the density wave theory.

September 23 — "Interferometry in a strong light"

  • Presenter: Cindy Regal, University of Colorado Boulder
  • Host: Paul Beale
  • Abstract: The best rulers are made from light!  Optical interferometry is at the heart of many precise measurements from gravitational wave searches to modern surface diagnostics and microscopy.  Generally one improves interferometer precision by increasing the light intensity, as well as by calming the many technical sources of noise that can perturb the mirrors or optical path.  However, at extreme levels of light strength where radiation forces are significant, a new and interesting disturbance should appear – the quantum shaking associated with random arrival of individual photons at a mirror of the interferometer.  This quantum backaction of light has been long foreseen in gravitational wave searches and played a formative role in quantum optics theory.  In this talk I will discuss an experiment in which we used a particularly compliant micro-scale, vibrating drum to finally observe this effect in an interferometer.  In this strong-light limit, interferometer mirrors can also be used as a nonlinear medium to manipulate light – for example to make squeezed light.  We are pursuing ways to translate more complex quantum states into light by coupling superconducting elements to an interferometer mirror.   

September 30 — "Quantum thermalization and many-body Anderson localization"

  • Presenter: David Huse, Princeton
  • Host: Leo Radzihovsky
  • Abstract: Progress in physics and quantum information science motivates much recent study of the behavior of extensively-entangled many-body quantum systems fully isolated from their environment, and thus undergoing unitary time evolution.  What does it mean for such a system to go to thermal equilibrium?  I will explain the Eigenstate Thermalization Hypothesis (ETH), which posits that each individual exact eigenstate of the system's Hamiltonian is at thermal equilibrium, and which appears to be true for many (but not all) quantum many-body systems.  Prominent among the systems that do not obey this hypothesis are quantum systems that are many-body Anderson localized and thus do not constitute a reservoir that can thermalize itself.  When the ETH is true, one can do standard statistical mechanics using the `single-eigenstate ensembles', which are the limit of the microcanonical ensemble where the `energy window' contains only a single many-body eigenstate.  These eigenstate ensembles are more powerful than the traditional statistical mechanical ensembles, in that they can also "see" the novel quantum phase transition in to the many-body localized phase, as well as a rich new world of many-body localized phases with symmetry-breaking and/or topological order.

October 7 — "The Space Economy"

  • Presenter: George Sowers, United Launch Alliance
  • Host: Markus Raschke
  • Abstract: Different questions about the space economy will be addressed.  Why is space so expensive?  What can be done to lower the cost of space activity? And most importantly, how can we create a self sustaining space economy?  A self sustaining space economy is the key to affordable space and to bring the vast resources of space into the economic purview of humankind.

    Dr. George F. Sowers is vice president of Advanced Concepts and Technologies for United Launch Alliance (ULA) headquartered in Denver, Colorado. In this role, Sowers is responsible for assessing product offerings, technology roadmaps, operations concepts, and business models that meet various potential customerfuture space architecture needs and buying approaches. The overall goal of Sowers’ team is to enable the design of the products, processes and infrastructure to meet our customers’ future requirements. Prior to this position, Sowers was the vice president of Human Launch Services.
    Before joining ULA, Sowers was director of Business Development for Lockheed Martin Space Systems Company.
    Sowers previously served as director of Mission Integration for the Atlas program and Chief Systems Engineer and director of the Systems Engineering and Integration Team (SEIT) for Atlas V development.
    Sowers began his career with Martin Marietta in 1981 as a flight design engineer on the Titan program.
    Sowers received his Bachelor of Science degree in physics from Georgia Tech in 1980 and his PhD in physics from the
    University of Colorado in 1988.
     

October 14 — "The Shining High-Energy Universe as a Plasma Astrophysicist's Playground"

  • Presenter: Dmitri Uzdensky, University of Colorado Boulder
  • Host: Paul Beale
  • Abstract: Most of the visible, shining Universe (the regular, non-dark matter) is made of plasma, a hot ionized gas that can carry electric currents and thus generate and interact with electromagnetic fields.  Cosmic plasmas are complex, turbulent, almost always immersed in magnetic fields and often collisionless, with nonthermal particle distributions. Many of the most spectacular phenomena in our magnetized plasma Universe involve rapid and bright high-energy bursts and flares, often exhibiting nonthermal spectra. These violent events are believed to be powered by just a few basic kinetic plasma processes: turbulence, shocks, and magnetic reconnection (rapid rearrangement of magnetic field topology, leading to a violent release of magnetic energy).  Studying them is the realm of Plasma Astrophysics.  Often, the intense radiation produced by these energy dissipation processes exerts an strong backreaction on them, controlling their energetics and dynamics and hence their observational signals.  However, radiative effects (e.g., radiative cooling, radiation pressure, photon-drag resistivity, pair creation) have so far been largely ignored in traditional theoretical studies.  My research program aims at building a coherent theoretical framework for the new frontier — Radiative Plasma Astrophysics — and at exploring its astrophysical applications.  Most of my research so far has focused on radiative effects on magnetic reconnection. I will give an overview of my group’s research in this area, including the development of new computational tools capable of investigating radiative kinetic plasma processes, and I will illustrate our work with several important astrophysical applications.

October 21 — "Pentaquarks: Quark Model Revisited"

  • Presenter: Tomasz Swarnicki, Syracuse University
  • Host: John Cumalat
  • Abstract: The LHCb experiment has recently reported the observation of pentaquark candidates: bound states of four quarks and an antiquark. Such objects have been predicted for over 50 years, but until recently believed not to exist. I will describe the bumpy road which led to this recent observation, starting from the birth of the Quark Model, through its spectacular success in describing known mesons and baryons and searches for quark structures made out of more than the minimal quark content. I will describe the LHCb pentaquark measurement and conclude with implications of the recent observations of tetraquark and pentaquark candidates on our understanding of the fabric of matter made out of quarks.

October 28 — "The new SI"

  • Presenter: David Newell, National Institute of Standards and Technology, Gaithersburg, Maryland
  • Host: Scott DIddams
  • Abstract: The International System of Units (SI from the French Le Système International d’Unités) is the universally accepted method of expressing physical measurements for world commerce, industry, and science. Though officially established in 1960, the origins of the present SI can be traced back to the creation of the decimal Metric System during the French Revolution. The SI has proven to be a living, evolving system, changing as new knowledge and measurement needs arise, and once again international consensus is building to advance the SI to reflect contemporary understanding of the physical world.  The new framework of the future SI will no longer be based on definitions of units such as the meter, kilogram, and second.  Instead it will adopt exact values for seven fundamental constants of nature upon which all SI units will be realized. Gone are the base units and their definitions.

November 4 — "New condensation and pairing mechanisms for high-Tc cuprate and unconventional superconductors inferred from muon and neutron experiments"

  • Presenter: Tomo Uemura, Columbia University
  • Host: Minhyea Lee
  • Abstract:Superconductivity of simple metals (Al, Sn, etc.) was explained by Bardeen, Cooper and Schrieffer who obtained Nobel Prize in 1972 for this contribution.  Soon after discovery of high-Tc superconductors in 1986 (which led to Nobel Prize to Bednorz and Mueller in 1987), we started muon spin relaxation (MuSR) measurements of the magnetic field penetration depth, and demonstrated nearly linear correlations between Tc and the superfluid density, which are manifest not only in cuprates but also in many other unconventional superconductors including Alkali doped C60, FeAs and some of the heavy-fermion systems.  The strong dependence of Tc on carrier density is not expected in the BCS condensation, but is a main characteristic of Bose Einstein Condensation.  Another important scaling of Tc is seen with the energy of the magnetic resonance mode measured by neutron scattering, which can be viewed as an excitation analogous to rotons in superfluid He. Rotons are short-range and short-time solid-like correlations, called soft mode, in superfluid state for which Landau was given Nobel Prize in 1962. This roton-like scaling is expected when condensed bosons are excited with phase fluctuations to another bosonic state, without breaking of a boson into two fermion pairs.  This again is different from Cooper pair-breaking excitations across the energy gap in BCS superconductors. We discuss these features and adopting BEC-BCS crossover picture for the cuprates, which I proposed in 1994, several years earlier than the burst of experiments by cold atoms.  Further consideration lead us to a possible pairing mechanism based on comparable spin and charge energy scales in cuparate and many other unconventional superconductors.

     

November 11 — "Polymer Drag Reduction"

  • Presenter: James Brasseur, Aerospace Engineering Sciences, University of Colorado (Formerly Penn State University)
  • Host: Mike Ritzwoller
  • Abstract: Fluid turbulence refers to a chaotic state of fluid motion that is dominated by strong nonlinearity among “eddies” spread over a broad range of length and time scales. It has been known since the 40’s that polymers injected at very low concentrations from the submerged surfaces of ships can dramatically reduce the drag on the ship hull by 40% or more, but that “polymer drag reduction” manifests only when the flow state is highly turbulent! The mechanical processes underlying the effect are so complicated that they are still under debate. Indeed, Pierre-Gilles DeGennes, who won the 1991 Nobel Prize in physics “for discovering that methods … can be generalized to more complex forms of matter, in particular to liquid crystals and polymers” wrote a paper on the topic that is still hotly debated by those who have researched the mechanisms. Why does the flow have to be turbulent and how do molecules orders of magnitude smaller than the smallest turbulent flow eddies cause such dramatic reductions in surface shear stress (i.e., drag)? I will address these questions using high-fidelity computer simulations of turbulent flow to argue that the essential mechanism is the suppression of momentum transport to the surface by strong interaction between polymer, turbulence and shear adjacent to the surface.

November 18 — "The Department of Physics and the German V-2 Legacy"

  • Presenter: R.C. "Merc" Mercure, Jr.
  • Host: John Cumalat
  • Abstract: The speaker will discuss the Department of Physics during the period of 1948 to 1956, the time when he was student in the Department. The preeminence in space science and space physics of the University, the Department of Physics, LASP as well as Ball Aerospace and Technology, Inc., can be directly traced back to 1947 when the Department of Physics won a contract to use captured German V-2 rockets to lift instruments above the earth’s atmosphere to study the sun. The early history of Ball Aerospace and of LASP is discussed.
    Dr. Ruel C. Mercure earned his PhD in physics in 1957, under William Rense. He is the 21st student at CU to earn a PhD in Physics.

November 25 Fall Break - No Colloquium

December 2 — "The Physics of Phagocytosis: How Polymerizing Polymers Drive Cell Engulfment of Particles"

  • Presenter: Jennifer Curtis, Georgia Institute of Technology
  • Host: Meredith Betterton
  • Abstract: Cell processes have evolved to be extremely robust. According to engineering principles, building a machine with robust function requires modular design and compartmentalization.  This is consistent with the observation that seemingly disparate cell processes like cell motility, phagocytosis and cytokinesis possess common sets of molecules that work together to achieve similar activities within a larger cellular event. For example, all of these processes require actin-driven membrane deformation, the exertion of contractile forces, and exquisite control of membrane tension. 
    With this broader perspective in mind, we investigate phagocytosis, the dramatic mechanical process by which individual cells engulf foreign bodies or debris.  It is critical to the immune response, being the hallmark behavior of white blood cells.   Considerable effort has been devoted to elucidating the biochemical pathways that direct phagocytosis.  However, mechanics of phagocytosis has received less attention.  We present a systematic study of mechanical signature of phagocytosis, including the forces and dynamics that occur during cell engulfment of a substrate, and the reproducibility from one phagocytotic event to another.  Our studies show that the majority of cells behave in a similar manner, having distinct phases of initial-contact, rapid spreading, and late-stage contraction.  Further the engulfment dynamics appear to collapse onto a single ‘master curve’ similar to that found for cell spreading in other unrelated scenarios. Our studies provide new territory for gathering details about the ‘modular’ actomyosin machinery that regulates phagocytosis and other cell mechanical processes.  In addition to addressing a long-standing puzzle about actin architecture in phagocytosis, we expect that our observations will provide insights into systems dependent on the actomyosin molecular machinery and chemo-mechanical coupling.

December 9 — "Programming colloidal self-assembly: Colloids with directional and DNA-mediated interactions"

  • Presenter: David Pine, NYU
  • Host: Ivan Smalyukh
  • Abstract: The self-assembly of colloids has been largely limited to spheres and rods with non-specific interactions and no directionality other than that imparted by a rod.  Recently a variety of new colloidal particles have been introduced, including particles with sticky patches, dimples, cavities, and other complex shapes, that enable assembly into spectrum of new structures.  Here we focus on the development of DNA-coated particles with highly specific, programmable, and thermally reversible interactions provides unprecedented control over particle assembly.  Of particular interest is the ability to assemble colloidal particles made from different materials, including polymers, inorganics, and metals, into complex hybrid structures with programmed particle placement.  A key recent development is the fabrication of DNA coatings that allow particles to bind and roll so that they can avoid kinetic traps and anneal into structures that minimize the free energy.

For more information about colloquia this semester, contact: Markus Raschke.

Colloquia are Wednesdays at 4:00 p.m. in DUAN G1B20, unless otherwise noted.

Coffee, tea and cookies will be available before regular colloquia beginning at 3:45 p.m. in DUAN G1B31.

January 14 — "Autonomous motility in soft active matter"

  • Presenter: Zvonomir Dogic, Brandeis University
  • Host: Meredith Betterton
  • Abstract: The laws of equilibrium statistical mechanics impose severe constraints on the properties of conventional materials assembled from inanimate building blocks. Consequently, such materials cannot exhibit spontaneous motion or perform macroscopic work; i.e., a fluid in a beaker remains quiescent unless driven by external forces. Inspired by biological phenomena such Drosophila cytoplasmic streaming, our goal is to develop a new category of soft active materials assembled from animate, energy-consuming building blocks. Released from the constraints of the equilibrium, such internally driven materials are able to change-shape, crawl, flow, swim, and exert forces on their boundaries to produce macroscopic work. Active liquid crystals can serve as a platform for developing novel material applications, testing fundamental theoretical models of far-from-equilibrium active matter and potentially even shedding light on self-organization of living cells.

January 21 — "Quantum matter without quasiparticles"

  • Presenter: Subir Sachdev, Harvard University
  • Host: Leo Radzihovsky
  • Abstract: The quasiparticle concept is the foundation of our understanding of the dynamics of quantum many-body systems. It originated in the theory of metals, which have electron-like quasiparticles; but it is also useful in more exotic states like those found in fractional quantum Hall systems. However, modern materials abound in systems to which the quasiparticle picture does not apply, and developing their theoretical description remains one of the most important challenges in condensed matter physics. I will describe recent progress in understanding the dynamics of two systems without quasiparticles: the superfluid-insulator transition of ultracold atoms, and the `strange metal’ found in the high temperature superconductors. Some of this progress relies on holographic methods which map non-quasiparticle quantum systems to the dynamics of black hole horizons.

January 28 — "Optical Multi-Dimensional Coherent Spectroscopy"

  • Presenter: Steven T. Cundiff, Physics, University of Michigan, JILA, National Institute of Standards and Technology & University of Colorado, Boulder
  • Host: Markus Raschke
  • Abstract: The concept of multidimensional Fourier transform spectroscopy originated in NMR where it enabled the determination of molecular structure.  In either NMR or optics, a sample is excited by a series of pulses. The key concept is to correlate what happens during multiple time periods between pulses by taking a multidimensional Fourier transform. The presence of a correlation, which is manifest as an off-diagonal peak in the resulting multidimensional spectrum, indicates that the corresponding resonances are coupled. Migrating multidimensional Fourier transform spectroscopy to the infrared and visible regimes is difficult because of the need to obtain full phase information about the emitted signal and for the phase difference between the excitation pulses to be stable and precisely incremented. I will give an introduction to optical two-dimensional coherent spectroscopy, using an atomic vapor as simple test system, but also show unexpected results due to atomic interactions. I will then present our use of it to study optical resonances in semiconductor nanostructures. In quantum wells, our results show that many-body effects dominate the light-matter interaction for excitons in semiconductors and provide a rigorous and quantitative test of the theory.  In quantum dots, there is inhomogeneous broadening due to size dispersion, however two-dimensional coherent spectroscopy can make size-resolved measurements without the need to isolate individual quantum dots.
     

February 4 — "Plasma-Based Particle Accelerators: There's Plenty of Room at the Bottom"

  • Presenter: Mike Downer, University of Texas, Austin
  • Host: John Cary
  • Abstract: Over the past few years, compact plasma-based particle accelerators have advanced sufficiently that it is no longer a pipe dream* to imagine a tabletop x-ray free-electron laser in every major university in the world, or proton cancer therapy on a scale that many hospitals could afford.  I will survey recent experimental highlights in the field that make these hopes more realistic than even a few years ago.  These include a milestone achieved recently using the Texas Petawatt Laser:  nearly mono-energetic acceleration of plasma electrons to 2 GeV with unprecedented sub-milliradian beam divergence.  I will discuss near-term prospects for improving plasma-based accelerators further, and for obtaining tunable x-ray radation from them.   Finally I will describe new holographic techniques that enable experimenters to visualize the electron density waves that lie at the heart of plasma-based accelerators.  Such 4D visualization, previously available only from intensive computer simulations, helps physicists understand how plasma-based particle accelerators work, and how to make them work better.

February 11 — "Spin and pseudospins in 2-dimensional semiconductors and heterostructures"

  • Presenter: Xiaodong Xu, University of Washington
  • Host: Markus Raschke
  • Abstract: Conventional semiconductors (e.g. Silicon and Gallium Arsenide) and their heterostructures are the foundation of condensed matter physics and present solid-state technologies, such as light emitting diodes, solar cells, and high speed transistors. Recently, new classes of quantum materials at 2-dimensional limit have been discovered, including atomically thin monolayers of graphite, boron nitride, and transition metal dichalcogenides (TMDs). These monolayer materials not only have remarkable physical properties on their own, but also they can be stacked together to form van der Waals heterostructures for new functionalities, offering unprecedented opportunities to explore new realms in materials science, device physics, and engineering. In this talk, I will focus on 2-dimensional semiconductors and their heterostructures. Fundamentally new properties in these structures include the relationship between electron spin, the "valley index" specifying which of the two inequivalent momentum states the electron occupies in the 2D lattice, and the "layer index" specifying which layer the electron is in when two monolayers form a bilayer. I will discuss the experimental progress towards understanding and optoelectronic control of spins and pseudospins in both monolayers and atomically-thin semiconducting heterostructures.

CANCELLED - February 18 — "What have we learned about the QGP from run I at the LHC?"

  • Presenter: Constantin Loizides, Lawrence Berkeley National Laboratory
  • Host: Jamie Nagle
  • Abstract: Nucleus-nucleus collisions at the Large Hadron Collider (LHC) occur at energies that enable the creation of a new state of matter, called the quark-gluon plasma (QGP), reaching energy densities similar to those achieved in the early universe shortly after the Big Bang. The system created in such collisions exhibits collective behavior characteristic of a strongly coupled, nearly inviscid fluid, which undergoes rapid three-dimensional expansion. Tomographic probes, e.g. involving the measurements of energetic partons or heavy flavor quarks, exhibit properties of the system consistent with expectations of hot partonic matter. I will discuss the most striking results from run I at the LHC, and will compare them
    with those from the Relativistic Heavy Ion Collider and to models, leading to an exploration of the QGP state over more than two orders of magnitude in collision energy.

February 25 — "Coherent Diffraction Imaging and Atomic Resolution Electron Tomography"

  • Presenter: Jianwei (John) Miao, Department of Physics & Astronomy and California NanoSystems Institute, University of California, Los Angeles
  • Host: Meredith Betterton and Markus Raschke
  • Abstract: For centuries, lens-based microscopy, such as light, phase-contrast, fluorescence, confocal and electron microscopy, has played an important role in the evolution of modern science and technology. In 1999, a novel form of microscopy, which is known as coherent diffractive imaging (CDI) or lensless imaging, was developed and transformed our traditional view of microscopy, in which the diffraction pattern of a non-crystalline object or a nanocrystal was first measured and then directly phased to obtain an image. The well-known phase problem was solved by combining the oversampling method with iterative algorithms. In the first part of the talk, I will present the principle of CDI and illustrate some applications using synchrotron radiation, X-ray free electron lasers and high harmonic generation.

    In the second part of the talk, I will present a general tomographic method for determining the 3D local structure of materials at atomic resolution. By combining scanning transmission electron microscopy with a novel data acquisition and image reconstruction method known as equally sloped tomography, we achieve electron tomography at 2.4 Å resolution and observe nearly all the atoms in a multiply-twinned Pt nanoparticle. We find the existence of atomic steps at 3D twin boundaries of the Pt nanoparticle and, for the first time, image the 3D core structure of edge and screw dislocations in materials at atomic resolution. We expect this atomic resolution electron tomography method to find broad applications in solid state physics, materials sciences, nanoscience, chemistry and biology.
     

March 4 — "Of Soot and Sunflowers"

  • Presenter: Chris Sorensen, Kansas State University
  • Host: John Cumalat
  • Abstract: Soot, the by-product of combustion, that smoky, black crap from chimneys, power plants and the inside of the tail pipe of my roadster, what scientist would ever bother to study soot? As a “particle physicist”, that’s what I do, and I find that soot has mysteries and beauties that can entertain any curiosity. In this talk I will describe some of my researches into soot and other aggregate structures; an unlikely journey of discovery to find fractal structures with non-Euclidian dimensionality, gel networks of graphene that tenuously span space and common Fibonacci themes for non-equilibrium phenomena such as sunflowers and soot.
    Christopher M. Sorensen is the Cortelyou-Rust University Distinguished Professor and a University Distinguished Teaching Scholar in the Departments of Physics and Chemistry (adjunct). He has won numerous teaching awards. In 2007 he was named the CASE/Carnegie Foundation United States Professor of the year for doctoral universities.
    He is also an active scientist with over 280 publications, six patents and three pending. In 2003 he won the Sinclair Award of the American Association for Aerosol Research, and he is a past president of that organization. He is a Fellow of the AAAR, the APS and the AAAS.
    Chris graduated from the University of Nebraska in 1969 where he was Phi Beta Kappa and a Woodrow Wilson Fellow. He was drafted and served in Vietnam. He earned his PhD in physics from the University of Colorado in 1977. In 2008 he was named a Norlin Distinguished Graduate of that university.

March 11 — "The early evolution of the Moon: Looking beneath the surface with GRAIL gravity data"

  • Presenter: Jeff Andrews-Hanna, Colorado School of Mines
  • Host: Shijie Zhong
  • Abstract: The geological record of the earliest history of the Moon is poorly preserved as a result of the heavy impact bombardment of the surface prior to 3.7 Ga.  However, the geophysical signatures of early lunar evolution are preserved in the subsurface.  Recent data from NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission is providing a view of the lunar subsurface at unprecedented resolution. Linear gravity anomalies reveal a population of ancient igneous intrusions that likely formed during an early period of thermal expansion of the Moon, providing an important constraint on lunar formation.  Later intrusive activity was dominated by the formation of circular or arcuate dikes within the ring structures surrounding the major impact basins.  In the absence of ring dikes, the gravitational signatures of tectonic offsets across the rings reveal the nature of the basin ring tectonics.  The largest magmatic-tectonic structure revealed by GRAIL is a quasi-rectangular set of linear density anomalies ~2500 km in diameter, encompassing the Procellarum region on the lunar nearside.  The gravitational signatures of the Procellarum border structures are consistent with volcanically flooded rift valleys, formed by extension driven by the gradual cooling and contraction of the Procellarum KREEP terrain. These and other observations from GRAIL are shedding new light on the early history of Earth's nearest neighbor.

March 18 — "Time-reversal-symmetry-breaking in unconventional superconductors"

  • Presenter: Aharon Kapitulnik, Stanford University
  • Host: Leo Radzihovsky
  • Abstract: BCS theory of conventional superconductivity describes pairing of spin-singlet time-reversed states, and is characterized by an order parameter which breaks U(1)-gauge symmetry leading to basic superconducting properties, such as the Meissner effect, persistent current and flux quantization. By contrast, unconventional superconductors exhibit additional broken symmetries, which often lead to distinct superconducting phases with unique properties. In this talk I will survey current searches for time reversal symmetry breaking (TRSB) in unconventional superconductors. After a brief discussion on the origin of TRSB in condensed matter systems I will introduce various ways to detect such effects, and in particular the use of magneto-optic like measurements that utilize the Sagnac interferometer that was invented in our group. I will show results on a variety of unconventional superconductors and discuss their implications to the determination of the possible pairing symmetry in each system.

Spring Break - No Colloquium March 25

April 1 — "Magnetic fields from the ocean floor to outer space"

  • Presenter: Margaret Kivelson, UCLA
  • Host: Mihaly Horanyi
  • Abstract:  Magnetic fields are ubiquitous in the universe. They control behavior of charged particles that fill most of space. They account for some of the structure observed in the universe. We earthlings live in a bubble in space, shielded by Earth’s magnetic field from direct interaction with most of the energetic particulate matter, some potentially destructive, that fills the solar system. This presentation will start with some historical background and will briefly discuss the generation of planetary magnetic fields, a subject still not fully understood.  Using data from spacecraft that have explored all the planetary bodies of the solar system, the talk will describe magnetic properties of some solar system bodies and how these properties affect their interaction with the plasma that surrounds them.

Physics Colloquium: Thursday, April 2 — "Quantum Tapestries" Sponsored by Annals of Physics

  • Presenter: Matthew Fisher, UC Santa Barbara
  • NOTE SPECIAL LOCATION: 11th Floor Commons Room
  • Host: Victor Gurarie
  • Abstract: Within each of nature’s crystals is an exotic quantum world of electrons weaving to and fro. Each crystal has its own unique tapestry, as varied as the crystals themselves. In some crystals the electrons weave an orderly quilt. Within others, the electrons are seemingly entwined in a entangled web of quantum motion. In this talk I will describe the ongoing eff orts to disentangle even nature’s most intricate quantum embroidery. Cutting-edge quantum many-body simulations together with recent ideas from quantum information theory, such as entanglement entropy, are enabling a coherent picture to emerge.

April 8 Joint Physics/APS Colloquium — "Detection of B-mode polarization at 150GHz and degree angular scales by BICEP2
and Keck Array"

  • Presenter: Clem Pryke, University of Minnesota
  • Host: Nils Halverson
  • Abstract: The theory of Cosmic Inflation postulates that our entire observable universe was spawned from a quantum fluctuation in an incredibly brief burst of hyper expansion. Inflation makes several predictions which appear to match features of the actual Universe in which we find ourselves, and, in addition, predicts that a background of gravitational waves will exist which may produce a specific observable feature in the polarization pattern of the Cosmic Microwave Background - the long sought B-mode polarization. Using data from a specialized radio telescope called BICEP2 operating from the South Pole in Antarctica our collaboration reported last year a highly significant detection of B-modes at 150GHz and few degree angular scales. However in a recently published joint analysis with the Planck space mission we find that, once an unexpectedly high level of polarized emission from dust grains in our own galaxy is taken into account, there is not currently significant evidence for a gravitational wave signal. I will describe the background, the results, and the continuing hunt for inflationary gravitational waves with the BICEP/Keck-Array experimental program.

April 15 — "A half-century of particle physics:  from CP violation to the Higgs boson"

  • Presenter: Bill Ford, University of Colorado, Boulder
  • Host: Paul Beale
  • Abstract: When as a grad student in 1964 I took my first particle physics course, the violation of CP symmetry had just been discovered, and the concept of "quarks" had newly been proposed.  In this talk I offer some personal perspectives on the evolution of the Standard Model of particle physics and some of the field's still-open questions.

April 22 — "Muon g-2 and the quest for TeV scale physics"

  • Presenter: Chris Polly, Fermilab
  • Host: Eric Zimmerman
  • Abstract: One of the most imperative questions in particle physics today is whether or not new physics will emerge at the few TeV scale.  Observational hints for new physics have arisen from several sectors with exciting theoretical implications that can potentially be explained by supersymmetry, dark matter, or other exotic models.  One of the most persistent hints comes from the Brookhaven muon g-2 experiment, where an ultra-precise measurement of the muon anomalous magnetic moment differs by >3 sigma from the theoretical expectation.  The anomalous magnetic moment of the muon provides a unique window into the TeV scale, and a new effort is underway at Fermilab to improve the experimental precision.  A review of the physics, the principles behind the experiment, and the incredible journey to bring the experiment to the point it is at today will be discussed.

April 29 — "Physics Textbooks Don't Always Tell the Truth

  • Presenter: Allan Franklin, University of Colorado, Boulder
  • Host: 
  • Abstract: Anyone who studies the history of physics quickly realizes that the history of physics presented in physics textbooks is often inaccurate. This is not necessarily a bad thing. The purpose of textbooks is to help students learn physics. An inaccurate history may serve a pedagogical purpose. It may help to explain concepts more clearly than the actual history. I believe, however, that it is important for those of us who teach physics to know the accurate history. In this talk I will discuss three episodes from the history of modern physics: 1) Millikan’s experiments on the photoelectric effect; 2) the Michelson-Morley experiment; and 3) the Ellis-Wooster experiment on the energy spectrum in β decay. Everyone knows that Millikan’s work established the photon theory of light and that the Michelson-Morley experiment was crucial in the genesis of Einstein’s special theory of relativity. The problem is that what everyone knows is wrong. The Ellis-Wooster experiment, on the other hand, is rarely discussed in physics texts, but it should be. In this talk I will present a more accurate history of these three experiments.

Special Colloquia

**SPECIAL Colloquium: Monday, January 12, Note date and location — "Topological soft matter: from linkages to kinks"

  • Presenter: Bryan Chen, Instituut-Lorentz for Theoretical Physics, Leiden University
  • Location: Duane G125
  • Host: Leo Radzihovsky
  • Abstract: Networks of rigid bars connected by joints, termed linkages, provide a minimal framework to design robotic arms and mechanical metamaterials built out of folding components.  These linkages may admit motions that perform useful functions.  Can these motions be made to be topologically robust?  I will explain this question and illustrate our answer with a chain-like linkage that, according to linear elasticity, behaves like a topological mechanical insulator whose zero-energy modes are localized at the edge. Simple experiments we performed using prototypes of the chain vividly illustrate how this edge mode can in fact propagate unobstructed all the way to the opposite end. Indeed, the chain is a mechanical conductor, whose carriers are nonlinear solitary waves, not captured within linear elasticity. This chain can be regarded as the simplest example of a topological mechanical metamaterial whose protected excitations are solitons, moving domain walls between distinct topological mechanical phases.  Live demonstrations on real toys will be performed.

**SPECIAL Colloquium: Monday, January 26 — "Broken-symmetry states in topological insulators"

  • Presenter: Yihua Wang, Stanford University
  • Location: DUAN G125
  • Host: Dan Dessau/Leo Radzihovsky
  • Abstract: Breaking the time-reversal symmetry (TRS) on the surface of a three-dimensional topological insulator (TI) transforms its metallic surface into a Chern insulator. The TRS-broken surface states are essential for many exotic emergent particles in condensed matter. In this talk, I will show broken TRS surface states of TI induced by magnetism and by light imaged with scanning microscopy and photoemission spectroscopy respectively. Our capability to manipulate mesoscopic magnetic structures as well as to shape ultrafast light pulses makes broken-symmetry states in TI promising platforms to simulate elusive fundamental particles such as magnetic monopoles and Majorana fermions.

**SPECIAL Colloquium: Thursday, January 29 — "Quantum Dynamics and Control of Chemical Reactions: From Cold Molecules to Quantum Biology"

  • Presenter: Timur Tscherbul, University of Toronto
  • Location: DUAN G130
  • Host: Andreas Becker
  • Abstract: Ultracold molecular gases hold the promise of revolutionizing atomic, molecular, and chemical physics by enabling high-resolution quantum control of molecular interactions with external electromagnetic fields. In the first part of this talk, I will present an efficient theoretical method for calculating low-temperature chemical reaction rates in the presence of electromagnetic fields. Using this method, I will show that electric fields with magnitudes <150 kV/cm can be used to control the total reaction cross sections, product state distributions, and the branching ratios for reactive vs inelastic scattering via electric-field-induced Feshbach resonances. In the second part of my talk, I will show how long-lived quantum coherences can be generated in multilevel atomic and molecular systems weakly illuminated by solar light. These noise-induced coherences arise due to Fano interference between incoherent pump transitions, and I will discuss the conditions under which such interference is likely to occur in real atomic and molecular systems. Finally, I will show that noise-induced coherences can play an important role in the initial stages of cis-trans photoisomerization of retinal in rhodopsin, the primary photoreaction in vision.

**SPECIAL Colloquium: Monday, February 2 — "Mechanics and Self-Organization of Biological Active Matter"

  • Presenter: Daniel Chen, Brandeis University
  • Location: DUAN G130
  • Host: Dan Dessau
  • Abstract: A remarkable feature of living matter is that mechanical motion at large length scales is routinely accomplished with exquisite precision by the cooperative action of millions of nanometer-sized molecular motors and fibers. Examples range from the way cells in our body divide to the way cilia lining our airways collectively beat to transport fluid. From a technological standpoint, it would be highly desirable to create artificial materials that could inherit, at least in part, this unique capability of living materials. Toward this goal, I will describe our creation of a versatile model system composed of microtubules, kinesin molecular motors, and polymer depletant that self-organizes into highly dynamic network of active bundles. Driven far from equilibrium by chemical energy from ATP hydrolysis, this active gel exhibits continuous structural remodeling, akin to the cell cytoskeleton, but has far fewer components and thus more amenable to experimental measurement and theoretical modeling. I will show that these active gels exhibit unique mechanical properties with no analogues in conventional equilibrium materials, including the ability to ‘cloak’ mechanical information at large length scales and to spontaneously flow under confinement. These properties exemplify new challenges and opportunities at the intersection of materials science, biology, and active matter physics.

**SPECIAL Colloquium: Tuesday, February 3 — "Beyond Independence: Emergent Neural Function and the Natural World"

  • Presenter: Ann Hermundstad, University of Pennsylvania
  • Location: JILA Auditorium
  • Host: Meredith Betterton
  • Abstract: The brain is composed of billions of neurons that exchange diverse patterns of electrical activity.  Collectively, these activity patterns encode information about the external environment (such as patterns of light intensity, chemical signals, and acoustic pressure waves), and they ultimately support a vast set of behavioral functions (such as the abilities to see in the dark, to learn to ride a bicycle, and to plan a career path).  I am interested in understanding how the anatomical and dynamical organization of neuronal populations facilitates these diverse functionalities, and more generally, why a particular organization is advantageous or disadvantageous.  Efficient coding—the notion that information processing systems are efficiently tuned to the statistical regularities of their natural inputs—provides a powerful organizing framework for approaching these questions.  I will highlight two applications of efficient coding in the visual system, where it is possible to both characterize the statistical structure of visual signals, and measure how these signals are encoded in populations of neurons.  In one application, we use behavioral experiments to measure human visual sensitivity to correlated textures (visual patterns with controlled statistical properties), and we show that this sensitivity is matched to the distribution of multipoint correlations present in natural scenes.  In another application, we use multi-electrode arrays to record the activity of visual neurons responding to natural and artificial movies, and we show evidence that the distribution of population activity patterns is matched to the statistical structure of natural movies.  Together, these studies provide evidence that the visual system is efficiently tuned to signals in the natural visual environment, and they raise a broad set of questions about the generality of these results across different neuronal and biological systems.

**SPECIAL Colloquium: Thursday, February 5 — "Dirac fermions and broken symmetries in topological crystalline insulators"

  • Presenter: Ilijia Zeljkovic, Madhavan Lab, Boston College
  • Location: DUAN G130
  • Host: Dan Dessau
  • Abstract: Topological crystalline insulators (TCIs) are a recently discovered class of topological materials which harbor massless Dirac surface states (SS). Theory predicts that these SS are protected by crystalline symmetries, and that SS electrons can acquire a mass if these symmetries are broken. In this talk, I will present our recent scanning tunneling microscopy (STM) investigations of the TCI Pb1-xSnxSe utilizing two different spectroscopic methods: quasiparticle interference imaging and Landau level spectroscopy. First, based on the interference patterns of scattered surface electrons, we uncover a distinct orbital texture of the Dirac bands in TCIs. Moreover, simultaneous imaging of the atomic and electronic structures reveals that a fraction of the Dirac electrons acquire mass due to a broken mirror symmetry. Our experiments suggest a novel pathway for manipulation of electrons in two-dimensional systems via lattice distortions.

**SPECIAL Colloquium: Monday, February 9 — "Many-Body Physics in the Attosecond World"

  • Presenter: Stefan Pabst, ITAMP, Harvard University
  • Location: DUAN G125
  • Host: Andreas Becker
  • Abstract: Ultrafast science is a young, vibrant, and highly interdisciplinary research field combining areas of biology, chemistry, and physics. Attosecond and strong-field physics focus on the electron motion in atoms, molecules, and solid state systems. In this talk, I discuss in more detail the importance of many-body processes in electronic motion as they appear in noble gas atoms when exposed to ultrashort and strong-field pulses. Furthermore, I explain the challenges and the perspectives of many-body theories in the strong-field regime. I show, in particular, how a time-dependent configuration interaction (TDCIS) approach can be applied to uniquely identify collective many-body effects in high-harmonic generation, and to discover an ultrafast decoherence mechanism that entangles the photoelectron with its parent ion within a few hundreds of attoseconds.

**SPECIAL Colloquium: Thursday, February 12 — "Emergent properties hidden in plain view: Strong electronic correlations at oxide interfaces"

  • Presenter: Jak Chakhalian, Center for Artificial Quantum Materials, University of Arkansas
  • Location: DUAN G130
  • Host: Dan Dessau
  • Abstract: Complex oxides are a class of materials characterized by a variety of competing interactions that create a subtle balance to define the lowest energy state and lead to a wide diversity of intriguing properties ranging from high Tc superconductivity to exotic magnetism and orbital phenomena. By utilizing bulk properties of these materials as a starting point, interfaces between different classes of complex oxides offer a unique opportunity to break the fundamental symmetries present in the bulk and alter the local environment. Harnessing our recent advances in complex oxide growth, we can combine materials with distinct or even antagonistic order parameters to create novel materials in the form of heterostructures with atomic layer precision. The broken lattice symmetry, strain, and altered chemical and electronic environments at the interfaces then provide a unique laboratory to manipulate this subtle balance and enable novel quantum manybody states not attainable in bulk. Understanding of these phases however requires detailed microscopic studies of the heterostructure properties. In this talk I will review our recent results on unit-cell thin nickelates, titanates and cuprate-manganite heterostructures to illustrate recentlyuncovered principles of rational materials design and control of collective quantum phenomena by the interface.
     

**SPECIAL Colloquium: Monday, February 16 — "Atomic giants in a new light: Quantum many-body physics with Rydberg atoms and photons"

  • Presenter: Thomas Pohl, Max Planck Institute for the Physics of Complex Systems, Dresden, Germany
  • Location: DUAN G130
  • Host: Andreas Becker
  • Abstract: The study of highly excited atoms has a long history in AMO physics, from the early days of quantum mechanics to the more recent development of cavity-QED. Lately, the advent of ultracold gases has ushered in a renaissance of Rydberg atom physics, allowing to create, probe, manipulate and utilize extreme atomic states with unprecedented precision. In particular, the combination of ultra-low temperatures, high densities and strong atomic interactions leads to rich physical behavior with promising applications in optical and information science.
    In this talk, I will outline different ideas to turn laser-driven Rydberg gases into a versatile platform for exploring exotic many-body phenomena in synthetic quantum systems, resembling quantum magnets, quantum fluids or quantum solids. Emerging correlations in such settings can have a substantial back-action onto the light field that excites the atoms. The resultant intricate interplay of light-matter and atom-atom interactions gives rise to unrivaled optical nonlinearities that open the door to manipulating light at the level of single quanta. I will present our progress towards understanding photon propagation in this new regime of quantum optics, from classical nonlinearities and few-photon applications to the quantum many-body physics of light.

**SPECIAL Colloquium: Thursday, February 19 — "Age of Oxides: New Physics and Foundations of Modern Technology"

  • Presenter: Gang Cao, University of Kentucky
  • Location: DUAN G130
  • Host: Dan Dessau
  • Abstract: Modern condensed matter physics research has produced novel materials with fundamental properties that underpin a remarkable number of cutting-edge technologies. Moreover, whoever discovers novel materials generally controls the science and technology that flows from them. It is now generally accepted that novel materials are necessary for critical advances in technologies. Transition metal oxides have recently attracted enormous interest within both the basic and applied science communities.  However, for many decades, the overwhelming balance of effort was focused on the 3d-elements and their compounds; the heavier 4d- and 5d-elements (which constitute two thirds of the d-transition elements listed in the Periodic Table) and their compounds have been largely ignored until recently. We review the unusual interplay between the competing interactions present in the 4d- and 5d-transition metal oxides, and how they offer wide-ranging opportunities for the discovery of new physics and, ultimately, new device paradigms.   

**SPECIAL Colloquium: Monday, February 23— "Many body localization: a new frontier for quantum statistical physics"

  • Presenter: Dr. Rahul Nandkishore, Princeton University
  • Location: DUAN G130
  • Host: Leo Radzihovsky
  • Abstract: The existing theory of quantum statistical mechanics describes open systems in contact with large reservoirs. However, experimental advances in the construction and control of isolated quantum systems have highlighted the need for an analogous theory of isolated systems. It has been realized that isolated quantum systems can support behavior which has no analog in open quantum systems. A prominent example is the phenomenon of many body localization.
    Many body localization occurs in isolated quantum systems, usually with strong disorder, and is marked by absence of dissipation, absence of thermal equilibration, a strictly zero DC conductivity (even at energy densities corresponding to high temperatures), and a memory of the initial conditions that survives in local observables for arbitrarily long times. Recently, my co-workers and I have demonstrated that many body localization also opens the door to new states of matter which cannot exist in thermal equilibrium, such as topological order at finite energy density, or broken symmetry states below the equilibrium lower critical dimension. We have also uncovered a host of unexpected properties, such as a set of universal spectral features and a non-local charge response, that have striking implications for fields as diverse as quantum Hall based quantum computation and quantum control. In this talk, I review the essential features of the many body localization phenomenon, and present some of the recent progress that I have made in this field. I also discuss the implications of these results for both theory and experiment.

**SPECIAL Colloquium: Thursday, February 26 — "Age of Oxides: New Physics and Foundations of Modern Technology"

  • Presenter: Michael Kolodrubetz, Boston University
  • Location: DUAN G130
  • Host: Andreas Becker
  • Abstract: Michael Fisher once wrote that “the task of theory is to ... understand the universal aspects of the natural world.” This goal has motivated physicists in understanding phenomena from phase transitions to topological physics. In this talk, I will discuss how the quest for universality has progressed in an emerging field of research: the dynamics of coherent quantum systems. Dynamics plays a crucial role in ultracold AMO experiments and has recently become important in solid state systems such as superconducting circuits, where coherence is necessary for protecting and manipulating quantum information. I discuss canonical examples of universality in these systems, such as eigenstate thermalization, many-body localization, and the dynamics near phase transitions. Then I detail recent work where, in collaboration with two experimental groups, we demonstrated that universal topological properties can be measured from the non-equilibrium response of superconducting qubits. With these experiments as a guidepost, I discuss how these robust probes can be extended to larger many-body systems, where they may be a useful tool in probing novel quantum states and performing metrology.

**SPECIAL Colloquium: Monday, March 2 — "From Quantum Communications to Small Quantum Computers"

  • Presenter: Graeme Smith, IBM TJ Watson Research Center
  • Location: DUAN G130
  • Host: Andreas Becker
  • Abstract: Physical information carriers obey quantum laws. Taking proper account of this fact has led over the past few decades to profound generalizations of both communication and computation theory. First, I’ll discuss the central question in the theory of quantum communication: What are the capabilities of a noisy quantum communication link? Addressing this question leads us to concepts like entanglement, a fundamentally quantum form of correlations which turns out to be a remarkably useful resource, new capabilities such as unconditionally secure cryptographic key agreement, and classically impossible kinds of synergy between independent communication links. Second, I’ll discuss two key questions in the race to build a quantum computer: what can we do with a small quantum computer, and how can we know that we’ve done it? These will be central questions in the coming decade as the size of quantum computing experiments begins to outstrip our capacity to do effective modeling on classical machines.

**SPECIAL Colloquium: Monday, March 9 — "Spatiotemporal control of the active forces that shape living tissues"

  • Presenter: Karen Kasza, Zallen lab, Memorial Sloan Kettering Cancer Center
  • Location: DUAN G125
  • Host: Matt Glaser
  • Abstract: The ability of multicellular tissues to physically change shape, move, and grow is a key feature of life. These processes are often accomplished by local movements or rearrangements of cells within the tissues. Many cell movements are actively driven by contractile forces generated in cells by the motor protein myosin II. During embryonic development, forces are patterned to orient cell movements, resulting in changes in tissue shape that build functional tissues and organs. To uncover how force-generation by myosin drives cell movement and determines the physical behavior of tissues, I use the fruit fly embryo as a model system, where polarized patterns of myosin activity orient cell movements and rapidly elongate the embryo. I will discuss how studying embryos made with engineered myosin variants allows us to dissect mechanisms underlying tissue behavior. In particular, I will describe how myosin variants with enhanced activity accelerate cell movement but, surprisingly, also alter the spatial pattern of forces and result in reduced tissue elongation. These experiments reveal that the levels and patterns of forces are controlled by the same biological cue and suggest a trade-off between the speed and orientation of cell movements within tissues. These studies of how forces shape the fruit fly embryo shed light not only on physical principles at work in active, living materials but also on how defects in cell movements contribute to human birth defects and tumor metastasis.

**SPECIAL Colloquium: Thursday, March 12 — "Revealing hidden symmetry breaking in strongly correlated matter"

  • Presenter: Darius Torchinsky, Caltech
  • Location: DUAN G130
  • Host: Daniel Dessau
  • Abstract: Essential to a microscopic understanding of strongly correlated materials is a clear picture of the relationship between their myriad quantum ground states. However, in phenomena ranging from unconventional magnetism to high temperature superconductivity, this picture is often obscured by the presence of broken symmetries hidden from view of existing experimental techniques. This may include hidden structural symmetries or tensor order parameters representing complex spatial arrangements of multipolar electric and magnetic moments. It may even include electronic forms oforder which come in and out of existence on ultrashort timescales, invisible to static probes. I will demonstrate how ultrafast time resolved and nonlinear optical methods can reveal hidden symmetry breaking in some of the most intensely researched strongly correlated materials of the past decade, including high-temperature superconductors, spin-orbit coupled transition metal oxides and heavy fermion materials, and I will discuss how the newly uncovered symmetries play a fundamental role in their physics.

**SPECIAL Colloquium: Thursday, March 19 — "Magnetic Resonance with Single Nuclear-Spin Sensitivity"

  • Presenter: Alex Sushkov, Harvard University
  • Location: DUAN G130
  • Host: Konrad Lehnert
  • Abstract: Our method of nanoscale magnetic sensing and imaging makes use of nitrogen-vacancy (NV) color centers a few nanometers below the surface of a diamond crystal. Using individual NV centers, we perform NMR experiments on single protein molecules, labeled with carbon-13 and deuterium isotopes. In order to achieve single nuclear-spin sensitivity, we use isolated electronic-spin quantum bits (qubits), that are present on the diamond surface, as magnetic resonance "reporters". Their quantum state is coherently manipulated and measured optically via a proximal NV center. This system is used for sensing, coherent coupling, and imaging of individual proton spins on the diamond surface with angstrom resolution, under ambient conditions, at room temperature. Our approach may enable magnetic structural imaging of individual complex molecules, and realizes a new platform for probing novel materials, and manipulation of interacting spin systems.

For more information about colloquia this semester, contact: Markus Raschke.

Colloquia are Wednesdays at 4:00 p.m. in DUAN G1B20, unless otherwise noted.

Coffee, tea and cookies will be available before regular colloquia beginning at 3:45 p.m. in DUAN G1B31.

August 27 — "Looking inside quantum materials with the Spallation Neutron Source"

  • Presenter: Dmitry Reznik, University of Colorado, Boulder
  • Host: Paul Beale
  • Abstract: High temperature superconductivity discovered in 1987 precipitated a revolution in solid state physics. All of a sudden physicists were forced to study complicated dirty materials with large unit cells and many interacting degrees of freedom. On a philosophical level, it became apparent that sometimes simple, striking, and very cool phenomena derive from complexity: Emergent phenomena in complex quantum materials became a new frontier in physics. Understanding these phenomena is often beyond traditional theory, although great progress is being made. It requires detailed direct knowledge of the inner workings of materials that can only be obtained through measurements. This necessity stimulated huge investments into new tools to study materials, many of which can rival high energy physics facilities. In fact solid state physicists took advantage of advances made by high energy physicists in accelerator science and built accelerator-based neutron and x-ray sources that can provide an extremely detailed picture of atomic and electronic structure, as well as dynamics of materials. I will describe some theoretical challenges of studying materials with complex interactions and tell about one of the newest large facilities for meeting the challenge from experimental side: the Spallation Neutron Source. It combines the most powerful pulsed neutron beams in the world with as a set of giant "eyes" that look into a wide range of materials by analyzing how neutrons bounce from investigated samples. I will give an example of a specific measurement from my research to illustrate its capabilities.

September 3 — "Light from Dark"

  • Presenter: Harry Nelson, University of California, Santa Barbara
  • Host: Eric Zimmerman
  • Abstract: We know from astrophysical evidence that the vast majority of matter in our Universe neither absorbs nor emits light. Does this `Dark Matter' have any relation to the strong, electromagnetic, or weak interactions that comprise our `Standard Model' of particle physics? I'll discuss the research program that seeks an answer to that question, by the attempt to detect direct interactions of the dark matter in laboratory experiments. I'll focus on the recent results obtained by the LUX experiment that operates a mile underground in an old gold mine in South Dakota. At the heart of the LUX experiment is the potential detection of light induced by the impinging dark matter particles I'll also discuss the recent decisions that have been made concerning future experiments, particularly the LZ experiment, that will follow LUX.

September 10 — "The Birth, Care, and Feeding of Cat States in Circuit QED: Quantum Jumps of Photon Parity"

  • Presenter: Rob Schoelkopf, Yale University 
  • Host: Jun Ye
  • Abstract: Dramatic progress has been made in the last decade and a half towards realizing solid-state systems for quantum information processing with superconducting quantum circuits. Artificial atoms (or qubits) based on Josephson junctions have improved their coherence times more than a million-fold, have been entangled, and used to perform simple quantum algorithms. The next challenge for the field is demonstrating quantum error correction that actually improves the lifetimes, a necessary step for building more complex systems. I will describe recent experiments with superconducting circuits, where we store quantum information in the form of Schrodinger cat states of a microwave cavity, containing up to 100 photons. Using an ancilla qubit, we then monitor the gradual death of these cats, photon by photon, by observing the first jumps of photon number parity. This represents the first continuous observation of a quantum error syndrome, and may enable new approaches to quantum information based on photonic qubits.

September 17 — "High Temperature Superconductivity – Insights from Einstein’s Electrons"

  • Presenter: Zhi-Xun Shen, Stanford
  • Host: Dan Dessau
  • Abstract: It is now over 100 years since superconductivity was discovered and it took 45 years before a theory was formulated by Bardeen-Cooper-Schrieffer (BCS). Once understood, the impact has been felt far behind superconductivity itself. High-temperature superconductivity in cupper oxides, with critical temperature well above what was anticipated by the BCS, was discovered 25 years ago and remains a major unsolved physics problem today.

    The challenge of this problem is symbolized by a complex phase diagram consists of intertwined states with extreme properties in addition to unconventional superconductivity. None of them can be described by conventional theory, thus compounding the difficulty to understand high-temperature superconductivity itself as these states are different manifestations of the same underlying physical system, making an integrated understanding a necessity.

    Angle-resolved photoemission spectroscopy (ARPES), derived from Einstein’s formulation of photoelectric effect, has emerged as a leading experimental tool to push the frontier of this important field of modern physics. Over the last two decades, the improved resolution and carefully matched experiments have been the keys to turn this technique into a sophisticated many-body physics tool. As a result, ARPES played a critical role in setting the intellectual agenda by testing new ideas and discovering surprises. This talk focuses on the insights we have gained on the rich phase diagram of the copper oxide superconductors – a pre-requisite for a complete understanding of high temperature superconductivity.

    References: 
    ZX Shen et al., Phys. Rev. Lett. 70 1553 (1993)
    D.S. Marshall et al., Phys. Rev. Lett. 76, 4841 (1996)
    A.G. Loeser et al., Science, 273, 325 (1996)
    K. Tanaka, Science 314, 1910 (2006)
    W.S. Lee et al., Nature 450, 81 (2007)
    M. Hashimoto et al., Nature Physics 6, 414-418 (2010)
    R. He et al., Science, 331, 1579 (2011)
    I. Vishik., PNAS 109, 18332 (2012)
    M. Hashimoto et al., Nature Physics 10, 483 (2014)
    M. Hashimoto et al., arXiv:1405.5199, to be published in Nature Materials, 2014

September 24 — "The Origin of the Mass of the Visible Universe"

  • Presenter: Zoltán Fodor, Eötvös Loránd University
  • Host: Anna Hasenfratz
  • Abstract: More than 99% of the mass of the visible universe is made up of protons and neutrons. Both particles are much heavier than their quark and gluon constituents, and the Standard Model of particle physics should explain this difference. A full ab initio calculation of these masses is carried out. To that end one uses the basic equations of the strong interactions on the lattice. Even the tiny mass difference between the neutrons and protons can be determined. The results completely agree with experimental observations. The generation of this hadronic mass is related to a transition in the early universe, which is also discussed.

October 1 — "Superconductors: Old and New"

  • Presenter: Robert Birgeneau, University of California, Berkeley
  • Host: Dmitry Reznik
  • Abstract: Solid State Physics is a field which continuously renews itself through the discovery of new materials and new phenomena. This has been particularly true for the subfield of superconductivity. We will review the progress in this field from Kammelingh Onnes's discovery of superconductivity in mercury in 1911 to the Bednorz-Mueller ground breaking discovery of high temperature superconductivity in the lamellar copper oxides in 1986 to recent work on the Fe arsenides and selenides. Research on superconductivity has produced theoretical insights which have implications not only for superconductivity itself but for systems as varied as liquid crystal gels to the fundamental constituents of the universe.

October 8 — "Chasing Away the Noise in Short-Pulse Lasers"

  • Presenter: Thomas Schibli, University of Colorado, Boulder
  • Host: Paul Beale
  • Abstract: Mode-locked lasers combined with phase-locking techniques have revolutionized precision measurements and spectroscopy applications alike. The technique that has driven these magnificent advances over a large range of scientific and engineering disciplines is indeed active feedback control, which rids a laser’s output of most amplitude and phase/timing fluctuations. Ideally, the ultimate noise level one could achieve in such systems would be solely determined by the coherence of an external reference, which is usually an ultra-narrow linewidth continuous-wave laser. In practice, the effectiveness of active stabilization relies on the available in-loop gain and bandwidth, both of which depend on the complex dynamics of pulse evolution, gain-photon coupling, and on the available actuators. While existing mode-locked lasers typically don’t limit the performance of an optical clock, they are typically the limiting link in applications that require good short-term stability. Such applications are currently enthusiastically pursued by many groups in form of timing dissemination at free electron lasers or for generating ultra-low noise microwaves.
    Based on our ongoing efforts in Boulder, I will describe our approach of making a low-noise frequency comb with the goal of reaching quantum limited noise performance from sub-Hz to the Nyquist frequency. I will describe a few basics of the laser dynamics to explain some of the technical and quantum mechanical noise sources in a laser and how they couple to phase noise in a frequency comb. This will lead us to design constraints of the laser and the development of novel actuators that enable very large feedback gains and bandwidths without the typical crosstalk of existing electro-optic modulators.

October 15 — "Unlocking Neutrino Properties with Long-Baseline Beams"

  • Presenter: Alysia Marino, University of Colorado, Boulder
  • Host: Paul Beale
  • Abstract: Over the past 15 years compelling evidence has emerged that neutrinos have non-zero masses and that neutrinos change from one flavor to another. Intense neutrino beams generated by particle accelerators are now being used in order to more precisely probe the spectrum of neutrino masses and mixing.
    This talk will briefly review the experimental evidence and the framework that describes neutrino oscillations. As an example of a man-made neutrino beam, it will focus on the Tokai-to-Kamioka (T2K) experiment, which creates a beam of muon neutrinos at J-PARC on the east coast of Japan. With two neutrino detectors, one located near the origin of the beam, and another located 295 km away, T2K has seen the disappearance of muon neutrinos and the appearance of electron neutrinos. The talk will conclude with a brief discussion of future long-baseline neutrino experiments, especially the efforts in the US to send a high-intensity beam of neutrinos from Fermilab to a former gold mine in South Dakota.

October 22 — "Curing Picophobia: LISA Pathfinder and Gravitational Wave Detection in Space"

  • Presenter: James Ira Thorpe, Goddard Space Flight Center, NASA
  • Host: Peter Bender
  • Abstract: The milliHertz band of the gravitational-wave spectrum offers an opportunity to study a rich variety of astrophysical systems and provide insight on galaxy formation, black hole growth, stellar evolution, gravitation, cosmology, and other areas. Observing in this band will require a large space-borne interferometer such as the Laser Interferometer Space Antenna (LISA). The LISA mission concept employs measurement techniques and technologies that are familiar to the precision measurement physics community but new to space flight. The LISA Pathfinder mission will provide an on-orbit demonstration of several of the key technologies for LISA-like missions. Led by the European Space Agency, with contributions from several European member states and from NASA, LISA Pathfinder expects to launch in 2015. A successful Pathfinder mission will open opportunities not only for gravitational wave detection, but also for other science applications of precision measurement in space. I will provide an overview of the Pathfinder mission, it's current status, and it's role in technology development for space-based gravitational wave observatories.

October 29 — "Seeing With the Nano-Eye: Accessing Structure, Function, and Dynamics of Matter on its Natural Length and Time Scales"

  • Presenter: Markus Raschke, University of Colorado, Boulder
  • Host: Paul Beale
  • Abstract: To understand and ultimately control the properties of functional materials, from molecular soft-matter to quantum materials, requires access to the structure, coupling, and dynamics on the elementary time and length scales that define the microscopic interactions in these materials. To gain the desired nanometer spatial resolution with simultaneous spectroscopic specificity we combine scanning probe microscopy with different optical, including coherent, nonlinear, and ultrafast spectroscopies. The underlying near-field interaction mediated by the atomic-force or scanning tunneling microscope tip provides the desired deep-sub wavelength nano-focusing enabling few-nm spatial resolution. I will introduce our generalization of the approach in terms of near-field impedance matching to a quantum system based on special optical antenna-tip designs. The resulting enhanced and qualitatively new forms of light-matter interaction enable measurements of quantum dynamics in an interacting environment or to image the electromagnetic local density of states of thermal radiation. Other applications include the inter-molecular coupling and dynamics in soft-matter hetero-structures, surface plasmon interferometry as a probe of electronic structure and dynamics in graphene, and quantum phase transitions in correlated electron materials. These examples highlight the general applicability of the new near-field microscopy approach, complementing emergent X-ray and electron imaging towards the ultimate goal of probing matter on its most elementary spatio-temporal level.

November 5 — "Student Understanding at the Upper Division: Thermal Physics and the Related Mathematics"

  • Presenter: John Thompson, University of Maine
  • Host: Steve Pollock
  • Abstract: Recent frontiers in physics education research include systematic investigations in the upper division.  I have been involved in collaborative efforts to conduct research on student learning in thermal and statistical physics.  The focus in thermodynamics has been on student ideas about the First and Second Laws and the associated concepts (e.g., work, heat, entropy); several studies yield additional insights about broader ideas, such as state functions.  Research in statistical physics has focused on the concepts underlying multiplicity and related ideas in probability.  Our research interests have included aspects of more advanced physics thinking, including connections between physics and relevant mathematics concepts in many of these areas, in order to explore the interaction of the mathematics and the physics in student understanding; examples include student interpretation of canonical representations, such as pressure-volume (P-V) diagrams and Taylor series expansions.  We have recently extended our work to investigate student understanding in analogous mechanical and chemical engineering courses.  Results from research are guiding the development of curricular materials designed for the upper division.

**SPECIAL COLLOQUIUM (Note Date and Location) Monday, November 10, Duane G125 — "Non-Dissipative Viscosity, Quantum Hall Effect and Topological Invariants"

  • Presenter: Victor Gurarie, University of Colorado, Boulder
  • Host: Paul Beale
  • Abstract: Topological states of matter are a rapidly developing area of research in condensed matter physics. Beginning from quantum Hall effect in the 80s-90s, and continuing with topological insulators a decade later, this field of study is now full of theoretical models with anticipated exotic behavior which await their experimental discovery and observation. After a brief introduction into this field, I will describe my work to study topological states of matter with a certain class of topological invariants first proposed in the context of topological insulators and now generalized to include potentially all topological states. I will also discuss the proposed relationship between these invariants and the non-dissipative viscosity, a quantity originally known from the study of plasmas in a magnetic field which more recently received attention in the context of quantum Hall effect. 

November 12 — “Mapping and Time-Stamping the Universe with the Pan-STARRS Sky Survey”

  • Presenter: Ken Chambers, University of Hawaii
  • Host: David Bartlett
  • Abstract: The Pan-STARRS Sky Survey is the first substantial synoptic digital sky survey, ranging from a few to thousands of measurements of some 6 billion astronomical objects. I will review the Pan-STARRS System and highlights of the scientific results to date. These include discoveries of Near Earth Objects, Comets, Kuiper Belt Objects, ultracold brown dwarfs; the 3-dimensional distribution of dust in the Milky Way, new features in the stellar and dynamical structure of the Milky Way, new galaxies in the local group, eclispsing binaries in M31 (critical for the distance ladder); ultraluminous supernovae, SnIa supernova and their constraints on dark matter, dark energy and quintessence; black hole tidal disruption events, high redshift quasars, and large scale structure. I will conclude with a brief description of the current Pan-STARRS NEO Survey, its expected data products, and the potential for identifing the source of gravitational wave events detected by LIGO.

    The Pan-STARRS1 Surveys have been made possible through contributions of the Institute for Astronomy of the University of Hawaii; the Pan-STARRS Project Office; the Max-Planck Society and its participating institutes: the Max Planck I nstitute for Astronomy, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching; The Johns Hopkins University; Durham University; the University of Edinburgh; Queen's University Belfast; the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated; the National Central University of Taiwan; the Space Telescope Science Institute; the National Aeronautics and Space Administration under Grant No. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate; the National Science Foundation under Grant No. AST-1238877; the University of Maryland; the Eotvos Lorand University; and the Los Alamos National Laboratory.

November 19 — "Restoration of Early Sound Recordings using Optical Metrology and Image Analysis"

  • Presenter: Carl Haber, Lawrence Berkeley National Laboratory
  • Host: Eric Zimmerman
  • Abstract: Sound was first recorded and reproduced by Thomas Edison in 1877. Until about 1950, when magnetic tape use became common, most recordings were made on mechanical media such as wax, foil, shellac, lacquer, and plastic. Some of these older recordings contain material of great historical interest, may be in obsolete formats, and are damaged, decaying, or are now considered too delicate to play.
    Unlike print and latent image scanning, the playback of mechanical sound carriers has been an inherently invasive process. Recently, a series of techniques, based upon non-contact optical metrology and image processing, have been applied to create and analyze high resolution digital surface profiles of these materials. Numerical methods may be used to emulate the stylus motion through such a profile in order to reconstruct the recorded sound. This approach, and current results, including studies of some of the earliest known sound recordings, are the focus of this talk and will be illustrated with sounds and images.
    Additional information can be found at irene.lbl.gov
  • Speaker Bio: Carl Haber is an experimental physicist.  He received his Ph.D. in Physics from Columbia University and is a Senior Scientist in the Physics Division of Lawrence Berkeley National Laboratory at the University of California. His career has focused on the development of instrumentation and methods for detecting and measuring particles created at high energy colliders, including Fermilab in the United States and at CERN near Geneva, Switzerland.  Since 2002 he, and his colleagues, have also been involved in aspects of preservation science, applying methods of precision optical metrology and data analysis to early recorded sound restoration.  He is a 2013 MacArthur Fellow and a Fellow of the American Physical Society and the John Simon Guggenheim Memorial Foundation.

November 26 Fall Break - No Colloquium 

December 3 — "The long and short of optical time keeping"

  • Presenter: Scott Diddams, University of Colorado, Boulder
  • Host: Markus Raschke
  • Abstract: In the past decade, clocks “ticking” at optical frequencies have surpassed in performance their much slower microwave counterparts.  The implication is that time intervals can now be sub-divided to below the femtosecond (10-15 s) that represents a typical optical cycle.   In this new generation of clocks, a laser plays the role of the pendulum, which has its frequency guided on long timescales by an atomic reference transition.  A laser frequency comb functions as the clockwork that accumulates optical cycles in order to ultimately realize a second.

    In this talk, I will provide an overview of the science and technology behind optical clocks, with a focus on practical and fundamental limitations to timing precision on long and short timescales.  In particular, I will highlight recent developments that provide a means to synthesize signals from the radio frequencies to millimeter waves with attosecond (10-18 s) timing precision.  Finally, I will attempt to offer some perspective on the challenges and opportunities for optical timekeeping that might lie ahead.  Along these lines, I will describe recent experiments with a new class of low-noise lasers and frequency combs based on monolithic microresonators.  Among their benefits, these chip-scale devices have the potential to significantly reduce the bulk, cost, and complexity of key components needed to move optical timing beyond the research lab.

December 10 — "Swellable Colloidal Particles are Swell"

  • Presenter: Arjun Yodh, University of Pennsylvania
  • Host: Ivan Smalyukh
  • Abstract: I will discuss soft matter experiments from my lab that explore fundamental issues in condensed matter physics. Briefly, soft materials deform easily when pushed, and their behavior is often dominated in surprising ways by entropy. Examples of soft matter include colloidal suspensions, emulsions, oil-water interfaces, polymer & surfactant solutions, liquid crystals, and mixtures thereof. These soft materials find applications in the paint, food science, & cosmetics industries, in practical control of complex fluid rheology & microfluidics, in cell biology, in high-tech problems such as photonics, printing & lithography, biochemical sensing, and in design of composites. Our recent work develops and takes advantage of a novel class of colloidal suspension composed of temperature-sensitive hydrogel particles; the temperature “knob” permits easy control of particle packing and simultaneous viewing by video microscopy [1]. These features, in turn, enable us to use colloidal crystals to answer fundamental questions about “how and where” crystal melting begins and about the mechanisms by which one crystal transforms to another during a solid-solid phase transition [2]. These features have also enabled us to critically explore open questions about disordered solids, e.g., how glasses rearrange internally when responding to mechanical stress [3]. After a broad introduction about soft matter and colloidal suspensions, I will describe these new experiments.

    REFERENCES
    [1]   Yunker, P.J., Chen, K., Gratale, M.D., Lohr, M.A., Still, T., Yodh, A.G., Reports on Progress in Physics 77, 056601 (Epub 2014).
    [2]   A.M. Alsayed, M.F. Islam, J. Zhang, P.J. Collings, A.G. Yodh, Science 309, 1207-1210 (2005); Y. Han, Y. Shokef, A. Alsayed, P. Yunker, T. C. Lubensky, A. G. Yodh,  Nature 456, 898-903 (2008); Peng, Y., Wang, F., Wang, Z., Alsayed, A.M., Zhang, Z., Yodh, A.G., and Han, Y., Nature Materials (Epub 2014).
    [3]   Chen, K., Ellenbroek, W.G., Zhang, Z.X., Chen, D.T.N., Yunker, P.J., Henkes, S., Brito, C., Dauchot, O., van Saarloos, W., Liu, A.J., and Yodh, A.G., Phys. Rev. Lett. 105, 025501 (2010); Chen, K., Manning, M.L., Yunker, P.J., Ellenbroek, W.G., Zhang, Z., Liu, A.J., and Yodh, A.G., Phys. Rev. Lett. 107, 108301 (2011); Still, T., Goodrich. C.P., Chen, K., Yunker, P.J., Schoenholz, S., Liu, A.J., and Yodh, A.G., Phys. Rev. E 89, (2014).

For more information about colloquia this semester, contact: Markus Raschke.

Colloquia are Wednesdays at 4:00 p.m. in DUAN G1B20, unless otherwise noted.

Coffee, tea and cookies will be available before regular colloquia beginning at 3:45 p.m. in DUAN G1B31.

January 15 — "Making a Clock"

  • Presenter: Jun Ye, University of Colorado Boulder, JILA
  • Host: Murray Holland
  • Abstract: The relentless pursuit of spectroscopy resolution has been a key drive for many scientific and technological breakthroughs over the past century, including the invention of laser and the creation of ultracold matter. State-of-the-art lasers now maintain optical phase coherence over many seconds and provide this piercing resolution across the entire visible spectrum. The new capability in control of light has enabled us to create and probe novel quantum matters via manipulation of dilute atomic and molecular gases at ultralow temperatures. For the first time, we control the quantum states of more than 1000 atoms so precisely that we achieve a more accurate and more precise atomic clock than any existing atomic clocks. With the clock accuracy and stability both reaching the 10-18 level, we now realize a single atomic clock with the best performance in both key ingredients necessary for a primary standard. We are also on the verge of integrating novel many-body quantum states into the frontiers of precision metrology, aiming to advance measurement beyond the standard quantum limit. Such advanced clocks will also allow us to test the fundamental laws of nature and find applications among a wide range of technological frontiers.

January 22 — "What to Do Now? How Individual Choices Add Up to Efficient Labor in Honeybee Colonies"

  • Presenter: Michael Breed, Department of Ecology and Evolutionary Biology, University of Colorado Boulder
  • Host: John Cumalat
  • Abstract: Social insects are among the most spectacularly successful animals. There are more individual social insects in terrestrial habitats than all other types of multicellular animals taken together. Key to their success is the ability to cooperate and efficiently perform tasks like nest construction, brood care, and food collection. Division of labor among worker social insects facilitates efficient task performance. Work in honeybee colonies is regulated by complex interactions among genetics, age, physiological state, and spatial location within the nest. Our work has focused on colony defense and on the work of middle-aged bees. Our findings give a window of insight into the how the social organization of honeybees generates efficient solutions for division of labor within colonies.

January 29 — "Solar Neutrinos and the Planets"

  • Presenter: Wick Haxton, UC Berkeley
  • Host: Paul Romatschke
  • Abstract: A problem in the standard solar model has arisen recently -- a disagreement between tests of surface metalicity (photospheric absorption lines) and interior metalicity (helioseismology). The discrepancy has an interesting connection to certain solar neutrino experiments (Borexino and especially SNO+), which may have the “reach” necessary to settle this question by directly measuring the amount of C and N in the Sun’s core. Such a measurement is important, as the discrepancy may be connected to a very interesting stage of solar system formation -- the last few million years of the nebular disk, when the process of planetary formation scrubbed between 50 and 100 earth masses of metal from the remaining nebular gas. The implications range from planet hunting to decoding the Sun’s structure. I will describe recent observations of “solar twins” that have made speculations of a planetary connection particularly interesting.

February 5 — "Mars Climate Change and the MAVEN Mission to Mars"

  • Presenter: Bruce Jakosky, LASP, University of Colorado Boulder
  • Host: Mihaly Horanyi
  • Abstract: The Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft launched on November 18, 2013, and will arrive at Mars and go into orbit on Sept. 22 this year. The goal of the mission is to study the Martian upper atmosphere composition and structure, and to measure the rate of escape of atmospheric gas to space. These observations will allow us to determine how much of the atmosphere has been lost to space throughout Martian history, and to better understand processes that relate to the history of the planet's climate and of its potential habitability by microbes. With the compelling observations of the geology and geochemistry of the surface that show evidence for a change in the Martian climate throughout time, the MAVEN observations will fill a large gap in our understanding of the Martian volatile and climate system. I'll talk about the development of the mission concept and hardware, current status of the spacecraft (as it's operating in space en route to Mars), and the planned operations and anticipated science results.

February 12 — "Pilot-Wave Hydrodynamics

  • Presenter: John Bush, MIT
  • Host: Leo Radzihovsky
  • Abstract: Yves Couder and coworkers have recently discovered that droplets walking on a vibrating fluid bath exhibit several features previously thought to be peculiar to the microscopic, quantum realm. These walking droplets propel themselves by virtue of a resonant interaction with their own wave field. Thus, the system is reminiscent of the double-wave pilot-wave dynamics envisaged by Louis de Broglie. New theoretical developments provide rationale for the complex behavior of the bouncing droplets, and yield a trajectory equation for the walking droplets. Experimental and theoretical results in turn reveal and rationalize the emergence of quantization and wave-like statistics from pilot-wave dynamics in a number of settings.

February 19 — "One, Two, Three, Many: Creating Quantum Systems One Atom at a Time"

  • Presenter: Selim Jochim, University of Heidelberg
  • Host: Cindy Regal
  • Abstract: Experiments with ultracold gases have been extremely successful in studying many body systems, such as Bose Einstein condensates or fermionic superfluids. These are deep in the regime of statistical physics, where adding or removing an individual particle does not matter. For a few-body system this can be dramatically different. This is apparent for example in nuclear physics, where adding a single neutron to a magic nucleus dramatically changes its properties. In our work we deterministically prepare generic model systems containing up to ten ultracold fermionic atoms with tunable short range interaction. In our bottom-up approach, we have started the exploration of such few-body systems with a two-particle system that can be described with an analytic theory. Adding more particles one by one we enter a regime in which an exact theoretical description of the system is exceedingly difficult, until the particle number becomes large enough such that many-body theories provide an adequate approximation.
    Our vision is to use our deterministically prepared tunable few-body systems as microscopic building blocks to prepare model systems that might help to gain insight into complex many-body systems in condensed matter or even QCD.

February 26 — "A Tabletop-scale Probe for TeV Physics: The Electric Dipole Moment of the Electron"

  • Presenter: David DeMille, Yale University
  • Host: Eric Cornell
  • Abstract: Time-reversal (T) symmetry is observed to be broken in K- and B-meson systems, in a manner consistent with the Standard Model (SM) of electroweak interactions. Violation of T-invariance makes it possible for elementary particles such as the electron to have an electric dipole moment (EDM) along their spin axis. Although the SM prediction for the electron EDM is too small to detect, extensions to the SM frequently predict EDMs within a few orders of magnitude of the current limits. I will describe the ACME experiment, which uses methods of atomic and molecular physics to detect the electron's EDM. We recently completed the most sensitive search for this quantity, finding a result consistent with zero but setting a limit an order of magnitude smaller than previous work. Remarkably, the result of this tabletop-scale experiment sets strong constraints on the existence of T-violating phenomena well above the TeV scale being probed at the Large Hadron Collider, and has a substantial impact on theories of physics beyond the Standard Model.

March 5 — "The Double Pulsar, Aurora Borealis and Testing Theories of Gravity"

  • Presenter: Maxim Lyutikov, Purdue University
  • Host: Dmitri Uzdensky
  • Abstract: The Double Pulsar - a system of two neutron stars in which both companions emit pulsed radio signals - is an excellent astrophysical tool to probe theories of gravity, stellar evolution and plasma physics in extreme conditions. Periodic eclipses seen in the system provided the first test of relativistic spin precession in strong gravity regime. A number of methods used in studying the interaction of the Solar wind with planetary magnetospheres can be directly applied to this amazing system.

March 12 — "Helium Rain and The State of Water Ice in Giant Planets Predicted with Ab Initio Simulations"

  • Presenter: Burkhard Militzer, University of California, Berkeley
  • Host: Shijie Zhong
  • Abstract: The Kepler satellite has detected over 3400 extrasolar planet candidates. Many of them are gas and ice giants, and some are even larger than Jupiter. This talk introduces ab initio simulations and discusses the state of matter at high temperature and pressure conditions that prevail in the interiors of giant planets. We describe how data from the Galileo mission to Jupiter has been combined with simulation results to demonstrate that helium rain occurs on this planet. We characterize water ice at megabar pressures and describe the phase transitions that we recently predicted. After formation of a giant planet, its core is exposed to metallic hydrogen at extreme pressure-temperature conditions and different core materials may dissolve. We were able to show that the cores of Jupiter and Saturn have been eroded. We conclude by discussing future directions in the field of ab initio computer simulations with applications in Earth and exoplanet science.

March 19 — "Signal Processing at Light Speed: Ultrashort Optical Pulse Generation with Arbitrary Waveforms

  • Presenter: Andrew Weiner, Purdue University
  • Host: Markus Raschke
  • Abstract: Lasers capable of generating picosecond and femtosecond pulses of light are now firmly established and widely deployed. Going beyond simple pulse generation, the programmable shaping of ultrafast laser fields into arbitrary waveforms has resulted in substantial impact, both enabling new ultrafast science and influencing practical applications in high-speed lightwave signal transmission. The lecture begins with a brief introduction to ultrafast optics and then specifically addresses methods permitting shaping of ultrafast laser fields on time scales too fast for direct electronic control, selectively surveying the field of pulse shaping from its inception more than twenty-five years ago until the present. Several examples illustrating a new area of science — in which researchers worldwide have used shaped laser pulses as tools to manipulate nanoscopic and quantum mechanical processes, including simple photochemical reactions — will be described. The final section of the lecture focuses on recent work from the Weiner laboratory in which pulse shaping is applied to investigate broadband frequency comb spectra generated through nonlinear optics inside chip-scale microresonators and to manipulate the wave packets of correlated photons.

March 26 — Spring Break; No Colloquium

April 2 — "MINOS + MINOS+ + CHIPS : Neutrino Oscillations at Work"

  • Presenter: Jennifer Thomas, University College, London
  • Host: Stephen Wagner
  • Abstract: The MINOS experiment has been the work horse of the Fermilab neutrino program and over the last 7 years has contributed to a number of seminal measurements of neutrino oscillation parameters. MINOS+ is starting now, a new phase of the experiment, to search for any-new-effect-it-can-find in the neutrino oscillation spectrum, but will also continue to contribute to the "standard parameter" measurements worldwide. Finally, a new vision for the Fermilab neutrino program could include further exploitation of this NuMI neutrino beam, the most powerful in the world. CHIPS is one such experiment, planned to measure delta-CP before anyone else does!

April 9 — "The 2013 Chelyabinsk Airburst Event"

  • Presenter: Mark Boslough, Sandia National Lab
  • Host: John Cumalat
  • Abstract: On Feb. 15, 2013, a small asteroid exploded about 40 km to the south of the Russian city of Chelyabinsk. Its proximity to a population center led to many injuries and widespread blast damage, but also yielded a plethora of serendipitous data in the form of video footage from security and dashboard cameras. Combined with seismic, infrasound, and satellite records, this data provides a rich and multi-faceted means to determine the projectile size and entry parameters, and develop a self-consistent model of the airburst.
    The best estimate of the kinetic yield (explosive energy) is 400-500 kilotons, making Chelyabinsk the most powerful such event observed since the 1908 Tunguska explosion (3-5 megatons). Analysis of video combined with subsequent on-site stellar calibrations enable precise estimates of entry velocity (19 km/s), angle (17° elevation) and altitude of peak brightness (29 km). This implies a pre-entry diameter of ~ 20 m and mass of ~12,000 tonnes.
    Hydrodynamic models can now be initialized with extremely accurate energy depositions at correct locations, and results can be compared to observations (such as timing and distribution of blast energy at the surface, and evolution of the trail) to validate the models and better understand the physical phenomena associated with airbursts. According to observation-based size/frequency curves, Chelyabinsk is approximately a once-per-century event Tunguska is about once-per-millennium. These two outliers suggest that the curves underestimate the frequency of large airbursts. Models suggest that they are more damaging than nuclear explosions of the same yield (traditionally used to estimate impact risk). The risk from airbursts is therefore greater than previously thought.
    Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.

For more information about colloquia this semester, contact: Tobin Munsat.

April 16 — "THz Investigations of Exotic Quantum States of Matter"

  • Presenter: Peter Armitage, Johns Hopkins University
  • Host: Dan Dessau
  • Abstract: “The underlying physical laws necessary for the mathematical theory of a large part of physics and the whole of chemistry are ... completely known…” ...or so was claimed in 1929 by P.A.M. Dirac shortly after the Schrodinger equation had been verified for few electron systems like H2 and He. Dirac continued that the difficulty in extending this success to larger systems is “only that the exact application of these laws leads to equations much too complicated to be soluble”. One could not have anticipated in 1929 that it is precisely this complexity and the resultant effects of 1024 particles acting in quantum mechanical unison that gives rise to a host of beautiful and striking phenomena in materials like superconductivity and magnetism. Like waves on the sea, these are collective phenomena with elementary excitations not easily reducible to the properties of the underlying electrons. Almost a century after Dirac, we know better; to paraphrase P. W. Anderson, more really IS different.
    The occurrence of exotic quantum phenomena that emerges on long length scales heightens the need for new experimental tools that probe finite, yet long time scales (compared to bare electronic ones). This talk will review recent advances in the area of THz spectroscopy and its application to exotic quantum states of matter. I will give examples of its use on material systems as diverse as high-temperature cuprate superconductors, 1D quantum spin chains, “heavy-fermion” magnets, and topological insulators. From the observations of quarks and meson-like bound states in spin-chains to Dirac strings and to nematic electronic liquid crystals, these systems are host to phenomena which are found repeated across the diverse length and time scales of physics. A desire to characterize materials in a novel fashion and answer specific scientific questions is driving the THz technology forward, while new technology is changing the kinds of questions we think to ask.

April 23 — "Testing Gravity via Lunar Laser Ranging"

  • Presenter: Tom Murphy, UC San Diego
  • Host: Tobin Munsat
  • Abstract: Forty years ago, Apollo astronauts placed the first of several retroreflector arrays on the moon. Laser range measurements between the earth and the moon have provided some of our best tests to date of general relativity and gravitational phenomenology--including the equivalence principle, the time-rate-of-change of the gravitational constant, the inverse square law, and gravitomagnetism. A new effort called APOLLO (the Apache Point Observatory Lunar Laser-ranging Operation) is now collecting measurements at the unprecidented precision of one millimeter, which will produce order-of-magnitude improvements in a variety of gravitational tests, as well as reveal more detail about the interior structure of the moon. This talk will include an overview of the science, a description of the instrument and its performance, evidence for dust accumulation on the lunar surface, re-discovery of a lost Soviet reflector, and an outlook for advancing the state of gravity tests in the solar system.

April 30 — "Quantum Computing and the Entanglement Frontier"

  • Presenter: John Preskill, Caltech
  • Host: Victor Gurarie
  • Abstract: The quantum laws governing atoms and other tiny objects seem to defy common sense, and information encoded in quantum systems has weird properties that baffle our feeble human minds. John Preskill will explain why he loves quantum entanglement, the elusive feature making quantum information fundamentally different from information in the macroscopic world. By exploiting quantum entanglement, quantum computers should be able to solve otherwise intractable problems, with far-reaching applications to cryptology, materials science, and medicine. Preskill is less weird than a quantum computer, and easier to understand.
    John Preskill is the Richard P. Feynman Professor of Theoretical Physics at Caltech.

Colloquia are Wednesdays at 4:00 p.m. in DUAN G1B20, unless otherwise noted.

Coffee, tea and cookies will be available before regular colloquia beginning at 3:45 p.m. in DUAN G1B31.

August 28 — "Ultracold Polar Molecules"

  • Presenter: Deborah Jin, JILA, University of Colorado Boulder
  • Host: Murray Holland
  • Abstract: Gases of atoms can be cooled to temperatures close to absolute zero, where intriguing quantum behaviors such as Bose-Einstein condensation and superfluidity emerge.  A new direction in experiments is to try to produce an ultracold gas of molecules, rather than atoms.  In particular, polar molecules, which have strong dipole-dipole interactions, are interesting for applications ranging from quantum information to modeling condensed matter physics.  I will describe experiments that produce and explore an ultracold gas of polar molecules. 

September 4 — "Superposition, Entanglement, and Raising Schrödinger’s Cat"

  • Presenter: David Wineland, NIST, University of Colorado Boulder
  • Host: Jun Ye
  • Abstract: Research on precise control of quantum systems occurs in many laboratories throughout the world, for fundamental research, new measurement techniques, and more recently for quantum information processing. I will briefly describe experiments on quantum state manipulation of atomic ions at NIST, which serve as examples of similar work being performed with many other atomic, molecular, optical (AMO) and condensed matter systems across the world. This talk is in part the “story” of my involvement that I presented at the 2012 Nobel Prize ceremonies.

September 11 — "Distributed Information Processing in Materials that Think"

  • Presenter: Nikolaus Correll, University of Colorado, Boulder
  • Host: Tobin Munsat
  • Abstract: Materials that think are enabled by recent advances in smart polymers, desktop manufacturing systems and miniaturization of computers.  These materials tightly integrate sensing, actuation, computation and communication in a periodic, amorphous fashion, which might enable revolutionary new composites with fully programmable capabilities.  The challenges in creating materials that think lie at the intersection of material science engineering and computer science, and - from a CS perspective - require advances in distributed algorithms for signal processing, control and routing of information.  I illustrate these challenges and recent advances by our group using three experimental case studies, all using identical computational infrastructure: (1) a soft robotic skin that can locate and classify textures by locally sampling, processing and classifying vibrations and route relevant information to a CPU using multi-hop networking; (2) A modular building block for creating intelligent walls and facade systems that can recognize complex gestures; and (3) variable-stiffness composites that can assume arbitrary shapes using simple actuation and local feedback control.  Albeit serving different functions at different scales, material and computational properties can be designed using an unified mathematical framework based on abstracting the computer network as continuous amorphous medium.

September 18 — "Quantum Phases of Matter"

  • Presenter: Michael Hermele, University of Colorado Boulder
  • Host: Paul Beale
  • Abstract: Much of condensed matter physics is based on the idea that two different systems can be in the same phase of matter, with its own characteristic properties.  Some phases of matter are intrinsically quantum in nature, including metals, band insulators and fractional quantum Hall liquids.  In recent years, it has become clear that we lack a satisfactory understanding even of the most basic question: "What constitutes a distinct quantum phase of matter?" This colloquium will describe my recent contributions toward an answer.

September 25 — "Topological Soft Matter: From Mathematical Theorems to Self-Assembly"

  • Presenter: Ivan Smalyukh, University of Colorado Boulder
  • Host: Paul Beale
  • Abstract: Topologically nontrivial fields and vortices frequently arise in superstring and quantum field theories, plasmas, optics, elementary particles, cosmology, condensed matter and atomic systems, etc. Their complex structures are expected to follow predictions of topological theorems and mathematical theories, such as the knot theory, but are rarely accessible to direct experimental visualization. On the other hand, soft condensed matter systems, such as colloids and liquid crystals, offer complexity in degrees of freedom and symmetries that allow for probing analogous phenomena on completely different scales, ranging from kinetics of atoms in glasses to cosmic strings in the early Universe. In my lecture, I will show examples of how CU students extend these possibilities by developing soft matter model systems to probe the scale-invariant interplay of topologies of surfaces, fields, and defects. This combination of topology and self-assembly paradigms emerges as an interdisciplinary scientific frontier of topological soft matter, potentially enabling scalable fabrication of composite materials with unusual properties.

October 2 — "Manybodypedia, Cluster-by-Cluster"

  • Presenter: Mackillo Kira, Universität Marburg, Germany
  • Host: Steven Cundiff
  • Abstract: Several seemingly unrelated research efforts are approaching the same central question: how does the quantum physics of interacting many-particle systems control macroscopic phenomena? This would be easy to answer if one only were able to solve the many-body Schrödinger equation exactly, a task that seems unsolvable for decades to come. The number of theoretic approaches and experimental setups are steadily increasing, which also makes the knowledgebase scattered. Therefore, it seems that one should start a thorough learning process, pedia, to combine and develop common many-body knowhow.
    In this talk, I present a tutorial “manybodypedia” by comparing semiconductors, atom condensates, and degenerate Fermi gases. I analyze them with correlated clusters that rigorously identify the elementary particle configurations, quasi-particles, within many-body systems. It turns out that the clusters also reformulate quantum optics in a form suitable for many-body investigations. The clusters can therefore be viewed as the “alphabets” combining the knowhow in quantum-optics and various many-body studies. As a synthesis of these concepts, I introduce the quantum-optical spectroscopy that produces unprecedented access to unexplored many-body physics.

October 9 — "Fierce Competition in a Correlated World"

  • Presenter: Kyle McElroy
  • Host: Paul Beale
  • Abstract: One of the most important states of matter we see around us is the Landau-Fermi liquid. In fact, this is the state of matter electrons have in metals and semiconductors which we rely on so much in our technology. Over the last several decades we have seen that introducing strong correlations and destroying this traditional conducting state leads to new and dramatic macroscopic states of matter. One playground for these new behaviors is doped Mott insulators, where Coulomb repulsion localizes electrons and competes with the itinerancy of introduced carriers. Such competition leads to strong atomic scale variation in the electronic properties which are a key component in understanding the resulting macroscopic phenomena.
    We have developed microscopic techniques for measuring the electronic structure on the atomic scale. With these probes we have investigated several materials in which atomic scale disorder plays a huge role in the electronic structure. I will discuss several examples where these probes have let us uncover the true microscopic nature of these macroscopic phases that are hidden on the bulk scale.

October 16 — "Crystallization Mechanisms in Biominerals"

  • Presenter: Pupa Gilbert, University of Wisconsin - Madison
  • Host: Meredith Betterton
  • Abstract: Biominerals include mollusk shells and the skeletons of algae, sponges, corals, sea urchins and most other animals. The function of biominerals are diverse: mechanical support, attack, defense, grinding, biting, and chewing, gravitational and magnetic field sensing, light focusing, and many others. The exquisite nanostructure of biominerals is directly controlled by the organisms, which have evolved to master the chemico-physical aspects of mineralization. By controlling the inorganic precursor nanoparticle size, packing, and phase transitions, organisms efficiently fill space, produce tough and hard structures, with micro- or macroscopic morphology optimized for their functions. Specifically, this talk will show the complex architecture of mollusk shell nacre, or mother-of-pearl, and how it is formed by animal-controlled self-assembly.

October 23 — "Black Holes–the Harmonic Oscillators of the 21st Century"

  • Presenter: Andrew Strominger, Harvard University
  • Host: Oliver DeWolfe
  • Abstract: In the twentieth century, many problems across all of physics were solved by perturbative methods which reduced them to harmonic oscillators. Black holes are poised to play a similar role for the problems of  twenty-first century physics. They are at once the  simplest and most complex objects in the physical universe. They are maximally complex in that the number of possible microstates, or entropy, of a black hole is believed to saturate a universal bound. They are maximally simple in that, according to Einstein's theory, they are featureless holes in space characterized only by their mass, charge and angular momentum. This dual relation between simplicity and complexity, as expressed in black holes, has recently been successfully applied to problems in a disparate variety of physical systems. I will give an introduction to the subject intended for a general audience.

October 30 — "Assessing the Cumulative Impact of Humans on the Landscape"

  • Presenter: James Syvitski, University of Colorado Boulder
  • Host: Tobin Munsat
  • Abstract: Humans are changing the Earth’s biophysical system — atmospheric and ocean climatology and chemistry, extent of snow cover, permafrost and sea-ice, glacier, ice-sheet and ocean volume, and indeed the hydrological cycle.  Some changes are truly global, represented by similar temporal trends — atmospheric greenhouse gases, global surface temperatures, nitrogen fluxes to the coastal zone, and species extinctions. 

    Striking is the extent and rate at which humans have modified Earth’s land surface; as just one example, humans are now the largest force in the movement of sediment — greater than ice, wind and water.  The traces of humanity (e.g. petroleum wells, geotechnical boreholes, mining-exploration holes, and deep-water wells) will last millions of years.  Historical deforestation and land clearing have greatly impacted soil erosion, hill slope failure and downstream sedimentation. 

    In this talk, I will discuss how, by any measure, we have entered a new geological era (labeled the Anthropocene), unique to the history of our planet. Some of these changes have crept up on us; others have gone unrecognized until recently. Global sustainability involves facing our risks both global and local and aligning governance with stewardship.

November 6   — "Poincaré's Tangle: The Topology of Chaos in State Space"

  • Presenter: Richard Kautz, NIST
  • Host: David Bartlett
  • Abstract: In 1889, while investigating the notorious problem of three gravitationally attracting bodies, Henri Poincaré discovered a tangled topological structure that we now recognize as the mathematical heart of chaotic motion. Poincaré would later write of his discovery, "One is struck by the complexity of this picture, which I do not even attempt to draw." Using the driven pendulum as an example and graphics as our primary tool, we will explore the topology of state space, where the trajectories of a system are visible as the streamlines of a flow. Saddle orbits within a flow are the keys to its topology and led Poincaré and his successors to understand that the trajectories of seemingly simple systems can be entwined in infinitely complex patterns. In 1960 Steve Smale introduced the horseshoe map as perhaps the simplest example of a state-space tangle and applied symbolic dynamics to demonstrate how chaos can be "as random as a series of coin flips."

November 13 — "Brilliant Blunders: From Darwin to Einstein – Colossal Mistakes by Great Scientists That Changed Our Understanding of Life and the Universe"

  • Presenter: Mario Livio, Hubble Space Telescope Science Institute
  • Host: Tobin Munsat
  • Abstract: Charles Darwin, William Thomson (Lord Kelvin), Linus Pauling, Fred Hoyle, and Albert Einstein were all brilliant scientists. Each made groundbreaking contributions to his field—but each also stumbled badly. For example, Darwin’s theory of natural selection shouldn’t have worked, according to the prevailing beliefs of his time. Not until Gregor Mendel’s work was known would there be a mechanism to explain natural selection. How could Darwin be both wrong and right? Astrophysicist Fred Hoyle dismissed the idea of a “Big Bang” origin to the universe. And Albert Einstein, whose name is synonymous with genius, speculated incorrectly about the forces that hold the universe in equilibrium—and that speculation opened the door to brilliant conceptual leaps. These scientists expanded our knowledge of life on earth, the evolution of the earth itself, and the evolution of the universe, despite and because of their errors. In this talk, I will discuss how the scientific process advances through error. Mistakes are essential to progress.

November 20 — "Mission 'Impossible': Exploring the Properties of Hot QCD Matter"

  • Presenter: Berndt Mueller, Duke University
  • Host: Paul Romatschke
  • Abstract: This lecture presents an overview of the status of the investigation of the properties of the quark-gluon plasma using relativistic heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). My lecture will focus on the insights that have been gained to date by the comparison experimental data from both facilities with theoretical calculations, highlight some of the present challenges, and end with an outlook on the experimental investigations that are planned for the next decade.

November 27 — Fall Break; No Colloquium

December 4 — "The National Solar Observatory — The Coming Decade of Discovery"

  • Presenter: Mark Rast, LASP, University of Colorado Boulder
  • Host: Tobin Munsat
  • Abstract: The move of the headquarters of the National Solar Observatory to the Boulder campus is underway, as is the construction of the four meter Advanced Technology Solar Telescope (ATST). This talk will focus on how these events promise, over the coming years, to transform solar physics and how it is taught at the university. The mission of the National Solar Observatory is to advance our knowledge of the Sun in the contexts of both stellar astrophysics and solar influences. The ATST will contribute by providing diffraction limited spectropolarimetric observations of the solar photosphere, chromosphere, and corona, resolving for the first time the fundamental interactions between solar magnetic fields and the dynamic plasma on scales below 0.1 arcsec. The aim is to elucidate the magnetohydrodynamic underpinnings of the solar dynamo as well as the reconfiguration of magnetic fields during flare and coronal mass ejection events. Since research in solar physics requires a knowledge base that is both wide-ranging and carefully focused, it poses challenges to effective graduate education. We will describe these and ongoing efforts to address them through a distributed program.

December 11 — "Science with 800,000 Collaborators: Tales from the Zooniverse"

  • Presenter: Chris Lintott, University of Oxford, UK
  • Host: Paul Romatschke
  • Abstract: The Zooniverse is the world's largest and most successful scientific crowdsourcing platform, engaging more than 800,000 volunteers in tasks including classifying galaxies, discovering planets and mapping star formation in the Milky Way. This talk will present highlights from the last six years, including the serendipitous discovery of galaxy-scale light echoes, and explain how an unusual set of bulgeless spiral galaxies identified by Galaxy Zoo volunteers is informing models of galaxy formation and feedback. The talk will also set out the future for this massively distributed effort in the world of future facilities such as the LSST and SKA.

For more information about colloquia this semester, contact: Tobin Munsat.

Colloquia are Wednesdays at 4:00 p.m. in DUAN G1B20, unless otherwise noted.

Coffee, tea and cookies will be available before regular colloquia beginning at 3:45 p.m. in DUAN G1B31.

January 16 — "Small Modular Nuclear Reactors: A Better Way to Go?"

  • Presenter: Jerry Peterson, University of Colorado Boulder
  • Abstract: About 13% of global electricity is derived from nuclear fission, and many new plants are under construction around the world. These tend to be very large, producing over a GW of electricity, costing billions, and taking many years to construct, piece-by-piece, on site. Popular opposition has led some nations to plan to discontinue their reliance on such facilities. There is also a large market, in principle, for small nuclear power plants, for remote communities, military bases, mines, and oilfields. Many firms are now developing Small Modular Reactors (SMR), which could be mass produced and shipped as sealed units, with high resistance to meltdown and proliferation concerns. The physics and engineering principles were demonstrated half a century ago, and modern methods indicate a bright future for SMR. This talk will emphasize the context and opportunities, but not the detailed designs, since the market is just opening.

January 23 — "Atoms in Optical Lattices: Cold Atomic Gases as Condensed Matter"

  • Presenter: William D. Phillips, Quantum Measurement Division, Physical Measurement Laboratory, National Institute of Standards and Technology
  • Host: Jun Ye
  • Abstract: An atomic-gas Bose-Einstein Condensate, placed in the periodic light-shift potential of an optical standing wave, exhibits many features that are similar to the familiar problem of electrons moving in the periodic potential of a solid-state crystal lattice. Among the differences are that the atoms in an optical lattice offer possibilities for measurement and control that are not readily available in traditional condensed systems. Experiments that are difficult or impossible with solids are often straightforward with optical lattices, sometimes with surprising results. Among these are single-particle effects like Bloch oscillations and many-body problems like the Hubbard Model and the Mott insulator transition. Cold atomic gases hold the promise of being quantum simulators of calculationally intractable problems of both fundamental and practical interest.

January 30 — "The Physical Genome"

  • Presenter: Rob Phillips, Caltech
  • Host: Leo Radzihovsky
  • Abstract: The ability to read the sequence of genes and genomes has transformed the face of biology. However, as part of the copying, storage, transfer and reading of the genetic information they harbor, genomes are subject to constant physical manipulation. In this talk, I will describe two case studies that illustrate the rich interplay between the information content of genomes and their behavior as physical objects. The first example will focus on how the genomes of viruses are packed within the tiny confines of the viral capsid and how that DNA comes out again once the virus infects a host. The second example will focus on the statistical mechanics of how cells make decisions by manipulating their genomes through protein binding.

February 6 — "Knots in Light and Fluids"

  • Presenter: William Irvine, Physics, University of Chicago
  • Host: Leo Radzihovsky
  • Abstract: To tie a shoelace into a knot is a relatively simple affair. Tying a knot in a field is a different story, because the whole of space must be filled in a way that matches the knot being tied at the core. The possibility of such localized knottedness in a space-filling field has fascinated physicists and mathematicians ever since Kelvin’s 'vortex atom' hypothesis, in which the atoms of the periodic table were hypothesized to correspond to closed vortex loops of different knot types. Perhaps the most intriguing physical manifestation of the interplay between knots and fields is the existence of knotted dynamical excitations. I will discuss some remarkably intricate and stable topological structures that can exist in light fields whose hydrodynamic-like evolution is governed entirely by the geometric structure of the field. I will then turn to experimental hydrodynamics: how to make knotted vortex loop configurations in fluids and how they evolve once made.

February 13 — "Irreversibility and the Second Law of Thermodynamics at the Nanoscale"

  • Presenter: Christopher Jarzynski, University of Maryland
  • Host: Leo Radzihovsky
  • Abstract: What do the laws of thermodynamics look like, when applied to microscopic systems such as optically trapped colloidal particles, single molecules manipulated with laser tweezers, and biomolecular machines? In recent years it has become apparent that small systems far from thermal equilibrium satisfy a number of strong and unexpected laws. In particular, a proper accounting of fluctuations allows us to rewrite familiar inequalities of macroscopic thermodynamics as equalities. I will describe some of this progress, and will argue that it has refined our understanding of the second law and the thermodynamic arrow of time.

February 20 — "A Close-Up of Synthetic Quantum Matter"

  • Presenter: Markus Greiner, Harvard University
  • Host: Leo Radzihovsky
  • Abstract: Ultracold atoms in optical lattices enable experimenters to create and study synthetic quantum matter, opening a window into the fascinating world of many-body quantum physics. With quantum gas microscopy we are now able to take the control of atoms in an optical lattice to the next and ultimate level of high fidelity addressing, manipulation and readout of single particles. I will present microscopic studies of strongly correlated quantum matter and the first realization of quantum magnetism in an optical lattice. This work opens a wide range of new possibilities and brings the realization of exotic states of matter within experimental reach.

February 27 — "Twisting Atomic Gases into Novel Quantum Phases"

  • Presenter: Nigel Cooper, Cambridge University
  • Host: Victor Gurarie
  • Abstract: One of the most important techniques in the ultracold atom toolbox is the optical lattice: a periodic scalar potential formed from standing waves of light. Optical lattices are central to the use of atomic gases to explore strong-correlation phenomena related to condensed matter systems. I shall describe how optical coupling of internal states of an atom can be used to create new forms of optical lattice, which cause neutral atoms to behave as charged particles in a strong effective magnetic field. The resulting Lorentz force will twist the trajectories of atoms into tight circles, completely altering the collective behaviour of the gas. I shall explain the origin of this Lorentz force, and the possibilities these lattices offer to explore novel topological many-body phases using ultracold gases.

 

March 6 — "Splitting the Higgs Boson: Composite Models at the High-Energy Frontier"

  • Presenter: Ethan Neil, Fermilab
  • Host: Anna Hasenfratz
  • Abstract: The recent discovery of the Higgs boson at the Large Hadron Collider represents a triumph for the Standard Model of particle physics. However, from a theorist's perspective several puzzles remain, among them the stability of the Higgs mass and the identity of dark matter. Models in which the Higgs itself is a composite bound state can provide elegant solutions to these puzzles, but these composite systems are inherently strongly coupled, and as such they can be challenging to investigate. Numerical field theory, which has enjoyed enormous success as a tool for study of the strong nuclear force, can provide new insights and deeper understanding. In this talk, I will briefly discuss the most promising models of Higgs compositeness, and present recent large-scale simulation results targeting such models, with an emphasis on connections to experiment.

March 13 — "Cancer Risks from Low Doses of Radiation, or BEIR and Blight"

  • Presenter: Tom Johnson; Radiation Biology, Colorado State University
  • Host: Jerry Peterson
  • Abstract: Ionizing radiation is unavoidable, and has been a particular issue in Boulder due to the proximity of the Rocky Flats plant. The physics community should be a source of factual information and context for the public. Recently the National Academy of Sciences released the “Biological Effects of Ionizing Radiation Report VII” (BEIR) in 2006. The BEIR report provides a comprehensive examination of the risks of “low” levels of ionizing radiation. The goal of this talk is to provide a brief review of radiation risks within the context of background radiation and occupational radiation exposures. We will examine how the BEIR numerical estimates of cancer risks (blight) have been cited, used to set policy, as well as abused. Additionally, a brief review of background radiation, regulatory limits, and high dose effects will be provided. Next, an overview of the BEIR committee recommendations and the source of the recommendations will be presented. Recommendations on how to best use and abuse the risk estimates will round out the lecture.

March 20 — "Confronting the Dark Energy Crisis in Fundamental Physics"

  • Presenter: Christopher Stubbs, Harvard University
  • Host: Konrad Lehnert
  • Abstract: The discovery of the accelerating expansion of the Universe has precipitated a crisis in fundamental physics that lies along the intellectual fault line between quantum mechanics and gravitation. We have given the name "Dark Energy" to the origin of the gravitational repulsion that is driving this accelerating expansion. Dark Energy evidently comprises about 75% of the cosmic inventory. We are living through an intellectual revolution that has many parallels with the advent of quantum mechanics, but it's unclear when we will achieve a breakthrough in our understanding. I will review the current state of Dark Energy observations, and sketch out some possible scenarios for the future.

March 27 — Spring Break; No Colloquium

April 3 — "How Might a Fermi Surface Die?"

  • Presenter: Senthil Todadri, Massachusetts Institute of Technology
  • Host: Michael Hermele
  • Abstract: In the last many years a number of metallic solids have been studied that defy understanding within the principles of conventional textbook solid state physics. The most famous are the cuprate high temperature superconductors though many other examples have been found. In this talk I will argue that the mysterious properties of many such materials arises from an imminent `death' of their Fermi surfaces. I will discuss some theoretical ideas on how to kill a Fermi surface, and their implications for experiments.

April 10 — "Plasma Nuclear Science: Nuclear Science in Hot, Dense and Dynamic Laboratory Plasmas"

  • Presenter: Dennis McNabb, Livermore National Laboratory
  • Host: Jerry Peterson
  • Abstract: Harnessing the energy of the sun and stars has been a science goal for the past ~60 years. The National Ignition Facility aims to be the first inertial confinement fusion facility to demonstrate a self-sustaining fusion burn, required to provide enough energy gain to make fusion energy feasible. The plasma environments created using laser-driven inertial confinement fusion implosions at the National Ignition Facility [1] and OMEGA Laser Facility [2] closely resemble the burning core of a star where the reactants are ionized and the electrons are in continuum states. The fusion reactions in these plasmas can also lead to an extremely high neutron brightness, ~10 orders of magnitude higher than produced in conventional accelerator and reactor facilities. The brightness is potentially high enough that a significant number of nuclei could sequentially undergo to two nuclear reactions within ~10 ps, providing a capability to study reactions on short-lived excited states. These capabilities offers some intriguing opportunities to improve our understanding of how the elements originated and the stars, stellar objects and stellar events that produce the elements. However, these facilities also present challenges because the plasma environment is a complex and dynamic system that is difficult to model. I will discuss some of these challenges and recent progress that has been made nuclear scientists to disentangle these complexities and exploit them to better understand the reactions that power the stars and create the elements that we observe in our world today.

 

April 17 — "Slippery Wave Functions"

  • Presenter: Leo Kadanoff, The James Franck Institute, University of Chicago
  • Host: Leo Radzihovsky
  • Abstract: Superfluids and superconductors are ordinary matter that show a very surprising behavior at low temperatures. As its temperature is reduced, materials of both kinds can abruptly fall into a state in which they will support a persistent, essentially immortal, flow of particles. These flows differ from anything in classical physics in that they produce neither friction nor resistance. A major accomplishment of Twentieth Century physics was the development of an understanding of this very surprising behavior via the construction of partially microscopic and partially macroscopic quantum theories of superfluid helium and superconducting metals. Such theories come in two parts: a theory of the motion of particle-like excitations, called quasiparticles, and of the persistent flows themselves via a huge coherent excitation, called a condensate. The quasiparticles are described by giving the quasiparticle energy as a function of the quasiparticle momentum. The condensate is described by giving its quantum wave function.

    Two people, above all others, are credited with for the construction of the quasi-particle side of the theories of these very special low-temperature behaviors: Lev Landau and John Bardeen.  Curiously enough, they partially ignored and partially downplayed the importance of the condensate wave function.  In both cases, this partial neglect of the actual superfluid or superconducting flow interfered with their ability to assess the subsidiary advances that occurred immediately after their celebrated work on quasiparticles.

    Some speculations are offered about the source of this unevenness in the judgments of these two leading scientists.

 

April 24 — "Dead Dinosaurs and Nuclear Wars"

  • Presenter: Brian Toon, Laboratory for Atmospheric and Space Physics, University of Colorado Boulder
  • Host: Paul Beale
  • Abstract: Sixty six million years ago a mountain sized chunk of rock, traveling at more than 10 times the muzzle velocity of an assault rifle, slammed into the shallow sea covering what is now the Yucatan Peninsula of Mexico. Shortly thereafter the 5th of the Earth’s great mass extinctions occurred. The energy released by the impact was comparable to having a 1-megaton nuclear explosion spaced every 5 km over the Earth’s surface. Massive tidal waves and earthquakes swept the Gulf of Mexico, and rock ejected from the crater carpeted the land as far away as Wyoming. However, a greater danger lay in the vaporized asteroid and coral from the bottom of the sea, which flew back into space in a massive fireball. After the material in the fireball recondensed into drizzle-sized droplets of rock it reentered the atmosphere over the entire Earth as a massive swarm of shooting stars. The shooting stars heated the upper atmosphere until it glowed like the heating bar in an electric broiler oven. The radiation from this hot gas and rock ignited all the land biomass on Earth, creating firestorms on a global scale, and broiled the dinosaurs alive. Then it became pitch-black, to dark even for cats to see, and much too dark for photosynthesis. Temperatures on the land fell below freezing. In the few years before the Earth recovered many species of plants and animals that were not broiled alive were driven to extinction by the cold weather. The food chain in the ocean collapsed because phytoplankton could no longer metabolize without sunlight, and the fish, ammonites and other larger creatures that depended on plankton starved to death. Many of these same phenomena may occur if there is a nuclear war. Nuclear explosions in cities would cause urban firestorms, killing large numbers of people. For example, 20 million Indians and Pakistanis might die directly from nuclear bomb blasts in a war involving 2/3 of their current arsenals. North Korea could cause as many casualties as the U.S. experienced in World War II, by exploding only 3 small atomic weapons over U.S. cities. The smoke from these firestorms would rise into the upper atmosphere, block sunlight, and cool the planet. The resulting cold temperatures would reduce or eliminate food production. Even a war between smaller powers, such as India and Pakistan, could cool the Earth to lower temperatures than any in thousands of years, damaging agriculture and triggering mass starvation, perhaps killing a billion people. A war between Russia and the US would likely create sub-ice age temperatures and kill the majority of the human population by starvation. Destruction of agriculture, starvation and large losses of life would sweep the planet even in places not attacked. Unfortunately, at present, we are not capable of stopping an asteroid from hitting the planet. It remains to be seen if we can prevent a nuclear conflict.

May 1 — "Theories and Models in Physics and Finance"

  • Presenter: Emanuel Derman, Director of Financial Engineering Program, Columbia University
  • Host: Markus Raschke
  • Abstract: Theories are attempts at an accurate description of some part of the world. Models are metaphors, analogies that explain the parts we don’t understand in terms of the parts we do. Models tell you what something is more or less like; theories try to tell you what something is. Models stand on someone else's feet. Theories stand on their own. Financial models are not theories; they are analogies, idealizations that always sweep dirt under the rug. Good models and good modelers have an obligation to make the the dirt explicit.

    Bio: EMANUEL DERMAN is Co-Head of Risk at Prisma Capital Partners and a professor at Columbia University, where he directs their program in financial engineering. His latest book is Models.Behaving.Badly: Why Confusing Illusion with Reality Can Lead to Disasters, On Wall Street and in Life, one of Business Week’s top ten books of 2011. He is also the author of My Life As A Quant, also one of Business Week's top ten of 2004, in which he introduced the quant world to a wide audience. He was born in South Africa but has lived most of his professional life in Manhattan. He obtained a PhD in theoretical physics from Columbia University, thereafter doing research on unified theories of elementary particle interactions. At AT&T Bell Laboratories in the 1980s he developed programming languages for business modeling. From 1985 to 2002 he worked on Wall Street, running quantitative strategies research groups in fixed income, equities and risk management, and was appointed a managing director at Goldman Sachs & Co. in 1997. The financial models he developed there, the Black-Derman-Toy interest rate model and the Derman-Kani local volatility model, have become widely used industry standards. In his 1996 article Model Risk Derman pointed out the dangers that inevitably accompany the use of models, a theme he developed in My Life as a Quant. Among his awards and honors, he was named the SunGard/IAFE Financial Engineer of the Year in 2000. He writes a fortnightly column called Models Behaving Badly for the Frankfurter Allgemeine Zeitung.

For more information about colloquia this semester, contact: Leo Radzihovsky

Colloquia are Wednesdays at 4:00 p.m. in DUAN G1B20, unless otherwise noted.

Coffee, tea and cookies will be available before regular colloquia beginning at 3:45 p.m. in DUAN G1B31.

August 29 — "Ultracold Fermions with Repulsive Interactions and Bragg Scattering in an Optical Lattice

  • Presenter: Wolfgang Ketterle, John D. MacArthur Professor of Physics, MIT-Harvard Center for Ultracold Atoms, Massachusetts Institute of Technology
  • Host: Jun Ye
  • Abstract: For a gas of fermions with repulsive interactions, a transition to a ferromagnetic phase has been predicted – the so-called Stoner model for itinerant ferromagnetism. However, any strong short-range repulsive potential necessarily features a weakly bound paired state. Our experiments show that the ferromagnetic transition does not take place, but is rather preempted by rapid pair formation. Our experimental study can be regarded as a quantum simulation of a Hamiltonian, for which even the qualitative phase diagram cannot be reliably obtained by computational methods. Second, I will show how light scattering can reveal the structure of atoms in optical lattices, analogous to X-ray or neutron scattering off solids.

September 5 — "Deliberate Discovery of Missing Materials and the 'Inverse Problem'"

  • Presenter: Alex Zunger
  • Host: Dan Dessau
  • Abstract: Condensed matter physics and material science have historically often proceeded via trial-and-error or even accidental discoveries of materials with interesting physical properties. One wonders if it makes sense instead to first declare the physical property you really want, then find which structure/material has this property? I will describe recent steps taken in this new field of "Inverse Design " where electronic structure theory is combined with biologically- inspired generic search strategies ("Material Genome Initiative"). Examples for nanostructures, magnetism, semiconductors and spectroscopy will be mentioned. Given that many materials that can be expected to exist, are in fact missing from the compilations of all materials previously made , one wonders if they are missing for a good reason (i. e, they are intrinsically unstable), or did people did not get around to making them yet, but they could have interesting properties? I will describe the way modern "first principles thermodynamics" can address this question of "Missing Materials".

September 12 — "Quantum Electro-Mechanics: A New Quantum Technology"

  • Presenter: Konrad Lehnert, JILA, University of Colorado Boulder
  • Host: Leo Radzihovsky
  • Abstract: That an object can be in two distinct places simultaneously is a consequence of quantum theory and a fact routinely invoked to account for the behavior of electrons and atoms. Nevertheless, these superpositions are in conflict with our everyday experience. What is the largest and most tangible object that can be prepared in such a superposition? This question has motivated researchers to fabricate micron-scale mechanical resonators and coax them towards the regime of quantum behavior. Indeed micro-mechanical devices recently reached the quantum regime. In this talk, I will describe how we use electricity to achieve the exquisite control and measurement of micro-mechanical resonators necessary to reach the quantum regime. Having entered this regime, we are now able to pursue many exciting ideas. We endeavor to use mechanical resonators as long-lived memories for the quantum states of electrical circuits. In addition, we are developing the technology to transfer quantum states between two incompatible systems via a mechanical intermediary. In the future, it may even be possible to test quantum theory itself in an unexplored region of mass and size scales.

September 19 — "Neutrino Mass and Oscillations: An Experimental View"

  • Presenter: Eric Zimmerman, University of Colorado Boulder
  • Host: John Cumalat
  • Abstract: The past fifteen years have seen a revolution in our understanding of the properties of the neutrino. A large set of experiments has observed two oscillation modes, indicating that there are three distinct mass states. In the last year, a third oscillation mode has been discovered, opening up future probes of new phenomena including CP violation. Despite the recent progress, however, much remains unknown about neutrinos and several experimental results remain difficult to reconcile with the simplest models. This talk will give an overview of what is known, what we're learning in this exciting era of measurements, and what we may be able to learn in the next decade and beyond.

September 26 — "Flatland with Cold Atoms"

  • Presenter: Jean Dalibard, Laboratoire Kastler Brossel, Département de physique de l'Ecole normale supérieure
  • Host: Eric Cornell
  • Abstract: In his world-famous novel "Flatland" published in 1884, the English writer Edwin Abbott imagined a social life in a two-dimensional world. With a very original use of geometrical notions, E. Abbott produced a unique satire of his own society. Long after Abbott's visionary allegory, microscopic physics has provided a practical path for the exploration of low-dimensional worlds.

    With the realization of quantum wells for example, it has been possible to produce two-dimensional gases of electrons. The properties of these fluids dramatically differ from the standard three-dimensional case, and some of them are still lacking a full understanding.
    During the last decade, a novel environment has been developed for the study of low-dimensional phenomena. It consists of cold atomic gases that are confined in tailor-made electromagnetic traps. With these gases, one hopes to simulate and understand more complex condensed-matter systems. The talk will discuss some aspects of this research, both from an experimental and a theoretical perspective. Connections with other domains of 2D many-body physics, such as the Quantum Hall phenomenon, will also be addressed.

October 3 — "Black Holes as Holograms of Strong Interactions"

  • Presenter: Oliver DeWolfe, University of Colorado Boulder
  • Host: Tom DeGrand
  • Abstract: Physical systems with strong interactions have long frustrated theorists, who are unable to turn to the traditional tools of perturbation theory for a solution. Recently, string theory — a theory designed to unify gravity with quantum mechanics — has produced evidence that black holes living in higher dimensions can provide a "holographic" description of certain strongly coupled phenomena, including systems related to quantum chromodynamics (the theory of the strong nuclear force) and the "strange metals" that include high-temperature superconductors, opening up a new avenue to exploring these fascinating systems. We describe these developments and some hopes for the future.

October 10 — "Bohr and his Atom a Century Later"

  • Presenter: Tom DeGrand, University of Colorado Boulder
  • Host: Leo Radzihovsky
  • Abstract: We are in the centenary year of the birth of what we still recognize as "modern physics," and it's worth spending a sentimental hour recalling how it all started. That's what the talk will be about. It should be no surprise, that what Bohr actually did was a little different than what textbooks say he did. Life is always more complicated than people want to think it is, and almost nobody finds the shortest path the first time out. To prepare yourself for the talk, think of an experiment you could do, with 1912 technology, which would tell you how many electrons hydrogen actually has.

October 17 — "The Higgs Particle, 40 Years of Searches: Is It Over?" **NOTE LOCATION CHANGE - G1B30**

  • Presenter: Tiziano Camporesi, CERN
  • Host: William T. Ford
  • Abstract: On July 4th the whole scientific world was aroused by news from CERN that the search for the Higgs boson might be over. In this colloquium we will introduce the reasons why this particle plays such a fundamental role in what is known as the Standard Model description of the subatomic world. We'll go through the challenges faced by the CMS experiment in its investigation of the various channels used to search for this elusive object, and why we are convinced of having found a new particle. The discovery ends a phase of the search and gives rise to new questions. The most urgent is whether the new particle has all the characteristics expected of the Higgs Boson. We'll conclude with an outline of what is being done to answer this question and what are the next fundamental questions raised by this discovery.

 

October 24 — "The National Ignition Facility: Pathway to Energy Security and the Physics of the Cosmos"

  • Presenter: Ed Moses, Lawrence Livermore National Laboratory
  • Host: Margaret Murnane
  • Abstract:The National Ignition Facility (NIF), at Lawrence Livermore National Laboratory in Livermore, California, is the world’s most energetic laser system. NIF is capable of producing over 1.8 MJ and 500 TW of ultraviolet light, 100 times more than any other operating laser. Completed in March 2009, it is maturing rapidly and transitioning into the world’s premier high-energy-density science experimental facility, while supporting its strategic security, fundamental science, and energy security missions.

    By concentrating intense laser energy into target only millimeters in length, NIF can, for the first time, produce conditions emulating those found in planetary interiors and stellar environments and creating fusion energy to power our future. The extreme conditions of energy density, pressure, and temperature will enable scientists to pursue fundamental science experiments designed to address a range of scientific questions, from observing new states of matter to exploring the origin of ultrahigh-energy cosmic rays. Early experiments have been successfully completed in support of materials equations of state, materials strength, and radiation transport in extreme temperature and pressure conditions.

    The National Ignition Campaign, an international effort pursued on the NIF, aims to demonstrate fusion burn and generate more energy output than the laser energy delivered to the target. Achieving this ignition goal will validate the viability of inertial fusion energy (IFE) as a clean source of energy. A laser-based IFE power plant will require advances in high-repetition-rate lasers, large-scale target fabrication, target injection and tracking, and other supporting technologies. These capabilities could lead to an operational prototype IFE power plant in 10 to 15 years. LLNL, in partnership with academia, national laboratories, and industry, is developing a Laser Inertial Fusion Energy (LIFE) baseline design concept and examining technology choices for developing a LIFE prototype power plant.This talk will describe the unprecedented experimental capabilities of the NIF, its role in strategic security and fundamental science, and the pathway to achieving fusion ignition to create a clean and secure energy future.

October 31 — "Exotic Quantum Critical Points: Beyond the Landau Paradigm"

  • Presenter: Matthew Hastings, Duke University
  • Host: Leo Radzihovsky
  • Abstract: The standard paradigm for describing phase transitions is the Landau paradigm of symmetry breaking. For example, the freezing phase transition between water and ice is associated with a breaking of translational symmetry due to the periodic lattice in the solid phase, while in a ferromagnet there is a phase transition associated with breaking of spin rotation symmetry as the local magnetic moments all line up, producing a macroscopic magnetic field. If the phase transition is second order, these symmetry properties determine the properties of the critical point between the two phases. However, it was proposed in the last decade that a very different class of "exotic" critical points may occur in quantum systems. These critical points are associated with the appearance of new particles with exotic properties: for example, particles that have a charge that is a fraction of the charge of an electron. I'll begin by reviewing the Landau symmetry breaking paradigm, and then turn to quantum systems and talk about how fractional charge can occur, before discussing recent numerical work with Melko and Isakov on these exotic points at the end.

November 7— "Five Decades of Lasers, Six Decades of Progress, and a Proposed Space Experiment to Test Einstein’s Assumptions"

  • Presenter: John Hall, University of Colorado, Boulder; JILA Fellow
  • Host: Jun Ye
  • Abstract: Even though this is the 51st year of the Laser, progress in its control and application in precision measurements is still accelerating. The Optical Frequency Comb technology exploded in 1999-2000 from the synthesis of advances in independent fields of Laser Stabilization, UltraFast Lasers, and NonLinear Optical Fibers, enabling a thousand-fold advance in optical frequency measurement, and searches (in the 16th digit) for time-variation of physical "constants". Current advances in ultra-precise locking are making possible stable optical frequencies defined by length and the speed of light, as well as by locking lasers to the resonant frequency of atoms. These two “clocks” represent our current prototypes of the clocks postulated by Einstein in 1905 in formulating the theory of Special Relativity, which can now be tested into the 18th decimal in a proposed Space-based experiment now being planned by our Space-Time Asymmetry Research collaboration (STAR).

November 14 — "Glacial Earthquakes and Glacier Dynamics in Greenland"

  • Presenter: Meredith Nettles, Columbia University
  • Host: Michael Ritzwoller
  • Abstract: Approximately half of the ice-mass loss currently occurring in Greenland is the result of dynamic processes leading to the export of calf ice from the Greenland Ice Sheet's marine margins. Rapid changes in glacier flow speeds, thinning rates, and terminus positions have been observed during the past decade, but remain poorly understood. Many of Greenland's largest glaciers also produce seismic signals equivalent in amplitude to those from earthquakes of magnitude ~ 5. The earthquakes show a strong seasonal signal, with most events occurring in late summer, as well as a secular variation, with 3-6 times as many earthquakes occurring in each recent year as in the early 1990s. We combine observations of globally recorded seismic signals with local geodetic observations at a large Greenland outlet glacier to obtain insight into the glacial-earthquake source process and the response of outlet glaciers to changing environmental conditions, including ice loss at the terminus and varying surface meltwater input. Systematic analysis of glacial earthquakes across Greenland shows that spatio-temporal trends in earthquake occurrence are closely linked to changes in ice dynamics, and allows us to use the earthquakes as a remote-sensing tool.

November 21— Fall Break; No Colloquium

 

November 28 — "Atomic and Molecular Processes in Strong Fields at the LCLS X-ray Laser"

  • Presenter: Phil Bucksbaum, Marguerite Blake Wilbur Professor in Natural Science; Director, Stanford PULSE Institute SLAC National Accelerator Laboratory, Stanford University
  • Host: Markus Raschke
  • Abstract: The Stanford Linac Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory is the world’s first hard x-ray free electron laser. Atomic and molecular physics experiments at LCLS have concentrated on studies of fundamental processes of photoionization and subsequent relaxation. The significant dynamical time scales involved are on the order of a few femtoseconds. Several strong-field and nonlinear effects have now been documented, and I will review the early results as well as the status of ongoing work.

December 5 — "Quantum is Different: Topology and Deconfinement in Solids"

  • Presenter: Ashvin Vishwanath, University of California, Berkeley
  • Host: Leo Radzihovsky
  • Abstract: The idea that states of matter are governed by new emergent laws – ‘More is Different’ – has been the guiding principle in the theory of solids.Largely, this was exemplified by symmetry breaking states such as superfluids and ferromagnets, which are ultimately described by a classical order parameter, despite being composed of quantum mechanical particles. However, experimental results over the last several years have impelled us to look for new forms of emergence that are intrinsically quantum mechanical. I will briefly discuss topological insulators, a newly discovered class of solids with strong spin orbit-interactions where topology forms the basis of a subtle distinction from ordinary insulators. Subsequently, I will talk about strongly interacting systems like frustrated magnets that realize even more exotic phases and how quantum entanglement can serve as a fingerprint of these novel states.

December 12 — "Defects with Character -- Majorana States in Condensed-Matter Systems"

  • Presenter: Bert Halperin, Harvard University
  • Host: Leo Radzihovsky
  • Abstract: Theory predicts the existence of some peculiar phases of quantum condensed matter systems, which have multiple degrees of freedom with very low energy, when localized “defects” are introduced. We shall focus on a class of these phases where each defect has half of a conventional degree of freedom, and the defects may be considered as sites for localized zero-energy states of a “Majorana fermion”. Such defects would also exhibit the intriguing property of “non-Abelian statistics” -- i.e., if various defects can be moved around each other, or if two identical defects can be interchanged, the result is a unitary transformation on the quantum mechanical state that depends on the order in which operations are performed but is insensitive to many other details.
    In my talk, I will try to explain these various concepts and discuss the attempts to realize them in condensed matter systems.

For more information about colloquia this semester, contact: Leo Radzihovsky

Colloquia are Wednesdays at 4:00 p.m. in DUAN G1B20, unless otherwise noted.

Coffee, tea and cookies will be available before regular colloquia beginning at 3:45 p.m. in DUAN G1B31.

For more information about colloquia this semester, contact: Leo Radzihovsky

January 18 — "picoSpin: Miniature NMR Spectrometers for Fun and Profit"

  • Presenter: John Price, Physics, University of Colorado Boulder, picoSpin, LLC
  • Abstract: Nuclear magnetic resonance spectroscopy has long been the preferred analytical tool of the organic chemist and its role is expanding into biochemistry. Every significant research organization in these fields hosts at least one high-resolution NMR spectrometer. Modern instruments are large and complex, they rely on liquid helium for cooling a superconducting magnet, and they cost from $0.5M to $5M each. Consequently, analytical applications of NMR spectroscopy have generally been confined to research laboratories. picoSpin is a Boulder start-up that is conducting a two-fold experiment: First, can we build a drastically smaller, cheaper, easier to use and less expensive high-resolution NMR spectrometer? Second, with its more limited capabilities, will this instrument find applications and a significant market? The answer to the first question is definitely yes. I will describe a $20k shoe-box sized NMR spectrometer and demonstrate during the talk that it can collect high-resolution proton spectra of organic liquids. The answer to the second question is still unfolding, but possible applications include chemical education, chemical manufacturing, quality control, bench use by research chemists and even field inspection of chemical fluids. I’ll also share some reflections on entrepreneurship from the perspective of an academic physicist.

January 25 — "Magnetic Resonance Physics Through a Cognitive Neuroscientist's Eyes"

  • Presenter: Marie Banich, Director of the Institute of Cognitive Science
  • Host: Jerry Peterson
  • Abstract: Magnetic resonance imaging has transformed the ability of neuroscientists to make linkages between behavior, brain structure, and brain function. In this talk, I will provide a very broad overview of what types of information these techniques can apply (and a rudimentary discussion of how they work) and why they have been so transformative for our field. In addition, I will speak to some limitations of these methods. Finally, a description on the new human magnetic resonance imaging system on the Boulder campus will be provided with an eye for how it might be a resource for the Physics community on campus.

February 1 — "From Viscous Fluids to Fermi Surfaces: The Lore of Anti-De Sitter Black Holes"

  • Presenter: Steve Gubser, Princeton
  • Host: Oliver DeWolfe
  • Abstract: Through the magic of string dualities, black holes in negatively curved spacetimes capture phenomena as diverse as viscous fluid dynamics and Fermi surfaces. I will give an overview of what these black holes look like and how they are used in applications to heavy ion collisions and aspects of condensed matter theory. Time permitting, I will discuss not only viscous fluid dynamics and Fermi surfaces, but also heavy quark energy loss and holographic superconductors.

February 8 — "Particle Physics Today"

  • Presenter: Lisa Randall, Harvard
  • Host: Oliver DeWolfe
  • Abstract: New developments in physics have the potential to radically revise our understanding of the world: its makeup, its evolution, and the fundamental forces that drive its operation. The Large Hadron Collider, which houses a 27 km ring accelerating protons to enormously high energies 100 meters underground, contains the most extensive and elaborate experiments ever built. In this lecture I will explore what theories predict and the nature of the experiments that study these tiny distances.

February 15 — "Magnetic Dynamos in the Lab: Progressing from Liquid Metal to Plasmas

  • Presenter: Cary Forest, University of Wisconsin
  • Host: Tobin Munsat
  • Abstract: Every astrophysical plasma is, as far as we can measure, magnetized and turbulent. How these magnetic fields spontaneously self-generate, through a process called the dynamo, and then act back on their surroundings is a central question in plasma astrophysics. Dynamos occur in plasmas that range from small and dense stellar plasmas to diffuse plasmas in galaxy clusters, and can have impacts that range from making life possible on Earth to controlling accretion onto black holes.
    Laboratory experiments on dynamos have been pursued for the last decade using large volumes of fast flowing, electrically neutral liquid metals to create conditions in which magnetic induction dominates resistive dissipation of electrical currents. In some cases, this creates a self-excited magnetic dynamo. This talk begins with an overview of the basics of dynamos, also demonstrating how lab experiments relate to natural dynamos in the Earth (liquid metal), and the Sun (plasma). As one example of this, our group has recently measured the turbulent electromotive force (through correlated fluctuations of velocity and magnetic field) in a 200 horsepower, 1 meter diameter liquid sodium experiment. We have directly observed how turbulence, on average, enhances the effective resistivity of the liquid metal and more rapidly transports magnetic flux. Recent experiments on a novel plasma device will then be described that establish the feasibility for creating a large, steady-state, fast flowing, weakly magnetized, hot plasma, exhibiting all of the critical parameters for dynamo studies. Remarkably, by changing plasma composition and density, the fluid Reynolds number can be independently controlled. Finally, we describe a much larger device, now under construction, which is projected to extend accessible parameter space to a regime much closer to astrophysical dynamos than liquid metals.

February 22 — "Quantum Networks of Trapped Atomic Ions"

  • Presenter: Chris Monroe, Physics, JQI and University of Maryland
  • Host: Jun Ye
  • Abstract: Trapped atomic ions are standards for quantum information processing, with each atom storing a quantum bit (qubit) of information in appropriate internal electronic levels. All of the fundamental quantum operations have been demonstrated between small numbers of atoms, and the central challenge now is how to scale the system to larger numbers of interacting qubits. The Coulomb interaction between trapped ions allows entangling operations through the collective motion of the ion crystal, which can be excited through the state-dependent optical dipole forces. When such an force is applied globally, an effective spin-spin interaction emerges whose sign and range can be precisely controlled with the laser, and any possible spin correlation function can be measured with standard state-dependent fluorescence techniques. This allows the quantum simulation of interesting spin models that possess nontrivial ground states for the investigation of quantum phase transitions, quantum frustration, and the emergence of spin liquid behavior. Such a quantum network may be limited in size by the stability and coherence of the motion of larger ion crystals, and current efforts are devoted to multiplexing to even bigger systems by shuttling ions through complex ion trap structures or mapping qubits onto photons that can allow the probabilistic entanglement between remotely-located atoms. Work on all of these fronts will be reported, including quantum simulations of magnetism with N=16 atomic qubits as well as progress on operating deterministic gates between atoms separated by macroscopic distances.

February 29 — "How Symmetric is the Electron? Looking for Out-of-roundness of 10-15 Femtometers"

  • Presenter: Eric Cornell, JILA, University of Colorado Boulder
  • Host: Leo Radzihovsky
  • Abstract: The electron's electric dipole moment (eEDM) will be sensitive to particle physics beyond the standard model. We make use of the extreme electric fields found within a molecular bond to pursue an experiment to set a new limit on eEDM at a level that should severely constrain supersymmetric models.

March 7 — The Geodynamo from a Whole Earth Perspective

  • Presenter: Peter Olson, Johns Hopkins University
  • Host: Shijie Zhong
  • Abstract: The geomagnetic field is generated through self-sustaining dynamo action in the Earth's core. The first part of this talk surveys the main components of the geodynamo, focusing on the roles of convection in the fluid outer core, solidification of the inner core, and heat transfer to the mantle in the dynamo process. The second part of this talk examines a defining property of the geodynamo, the phenomenon of magnetic polarity reversals, which represents the most extreme form of geomagnetic variability. Progress in resolving the history of geomagnetic reversals and the structure of the geomagnetic field during polarity transitions has been matched by recent advances in modeling the reversal process in the core using first-principles numerical dynamos. Numerical dynamos reveal that geomagnetic reversals are sensitive to convection in the core, Earth's rotation, and the interactions between the core and the mantle. Although individual geomagnetic reversals appear to be stochastic, their long-term sequencing includes time periods with frequent reversals alternating with long-lasting stable magnetic polarity superchrons over approximately 200 million year cycles. A proposed explanation for these ultra-low frequency cycles is the modulation of heat transport from the core to the mantle on geologic time scales.

March 14 — "Transport Experiments on Surface States of Topological Insulators"

  • Presenter: N.P. Ong, Princeton
  • Host: Minhyea Lee
  • Abstract: The topological surface states in 3D materials predicted by Kane, Mele and Fu were rapidly detected by surface sensitive spectroscopy (ARPES and STM). Transport experiments to investigate their properties have been more challenging. Following a brief introduction, I will survey experiments in which the surface states were first detected by magnetoresistance oscillations in Bi2Se3 and Bi2Te3. More recently, the hybrid Bi2Te2Se has emerged as the most attractive candidate for transport experiments. I will describe a recent experiment showing that the occupation of the surface Dirac cone can be tuned by liquid gating.

March 21 — "Once Upon a Time in Kamchatka: The Extraordinary Search for Natural Quasicrystals"

  • Presenter: Paul Steinhardt, Princeton
  • Host: Leo Radzihovsky
  • Abstract: A quasicrystal is an exotic state of matter with an atomic structure analogous to a Penrose tiling, exhibiting symmetries forbidden to crystals, such as five-fold symmetry in the plane and icosahedral symmetry in three dimensions. The concept of quasicrystals was first introduced twenty-eight years ago and over a hundred types have been synthesized in the laboratory by now. But could Nature have beaten us to the punch? The campaign to answer that question makes for one of the stranger scientific stories you are ever likely to hear.

March 28 — Spring Break; No Colloquium

April 4 — "Wiring up Quantum Systems: Fun with Artificial Atoms and Microwave Photons "

  • Presenter: Steve Girvin, Yale
  • Host: Leo Radzihovsky
  • Abstract: A revolution is underway in the construction of ‘artificial atoms’ out of superconducting electrical circuits. These macroscopic ‘atoms’ have quantized energy levels and can emit and absorb quanta of light (in this case microwave photons), just like ordinary atoms. Unlike ordinary atoms, the properties of these artificial atoms can be engineered to suit various particular applications, and they can be connected together by wires to form quantum ‘computer chips.’ This so-called ‘circuit QED’ architecture has given us the ability to test quantum mechanics in a new regime using electrical circuits and to construct rudimentary quantum computers which can perform certain tasks that are impossible on ordinary classical computers. [1] ‘Wiring up quantum systems,’ R.J. Schoelkopf and S.M. Girvin, Nature 451, 664 (2008).

April 11 — "A Little Big Bang: Strong Interactions in Ultracold Fermi Gases"

  • Presenter: Martin Zwierlein, Physics, MIT
  • Host: Leo Radzihovsky
  • Abstract: Fermions, particles with half-integer spin such as electrons, protons and neutrons, are the building blocks of matter. When fermions strongly interact, complex phenomena emerge, for example high-temperature superconductivity or superfluidity in neutron stars. Ultracold Fermi gases of atoms are a new type of strongly interacting fermionic matter that can be created and studied in the laboratory with exquisite control. For example, we can study the collision of "spin up" and "spin down" Fermi gases with the strongest interactions allowed by quantum mechanics. In equilibrium, direct absorption images of the trapped atomic gas reveal the entire thermodynamics of the system, including the transition into the superfluid state. Scaled to the density of electrons, superfluidity would occur far above room temperature. We were recently able to follow the evolution of fermion pairing from three to two dimensions, connecting quite directly to models of layered superconductors. Our measurements in and out of equilibrium provide benchmarks for current many-body theories and will help to understand other strongly interacting Fermi systems, such as high-temperature superconductors and neutron stars.

April 18 — "Topological Order and Long Range Quantum Entanglements -- From Origins to New Quantum States of Matter"

  • Presenter: Xiao-Gang Wen, Physics, MIT
  • Host: Leo Radzihovsky
  • Abstract: What is the origin of fractional charges and fractional statistics in FQH states? What is the origin of light? It turns out that long range entanglement is the reason why fractional charges and fractional statistics can appear FQH state. Long range entanglement is also the reason why waves that satisfy Maxwell equation can appear in some qubit (spin) systems. Long range entanglement also lead to a deeper understanding of gapped quantum phases. It allows us to obtain a classification of interacting topological insulators/superconductors, as well as the much more general symmetry protected topological phases, and intrinsic topological phases.

April 25 — "Redefining Snake Oil: Lessons Learned from Pythons that Could Benefit People"

  • Presenter: Leslie Leinwand, MCDB, University of Colorado Boulder
  • Host: Meredith Betterton
  • Abstract: The major research interests of Dr. Leinwand’s laboratory are the biology of inherited diseases of the heart and how gender and diet modify the heart. Recently, her work has focused on the extreme biology of the Burmese python and how this biology might be translated to therapeutics for human heart disease. In the wild pythons do not eat very often but when they do eat, they eat enormous meals that can equal their body mass. To digest such a meal, almost all organs in the body grow very rapidly and then regress in size just as rapidly. Her laboratory’s investigations into the mechanisms responsible for the increase in heart mass in Burmese pythons after a large meal have revealed information that may be applicable to the mammalian heart. They found that heart growth in pythons is characterized by cellular enlargement in the absence of cell proliferation and by activation of beneficial signaling pathways much like the process by which highly conditioned athletes increase the sizes of their hearts. Despite extremely high levels of circulating lipids, which would be toxic to the heart, the post-fed python heart does not accumulate fats. Instead, there is robust activation of pathways of fatty acid transport and oxidation combined with increased expression and activity of a cardioprotective enzyme. They also identified a specific combination of three fatty acids in python plasma that promotes beneficial heart growth when injected into either pythons or mice. The long term goal is to promote heart health using the biology of the python.

May 2 — "The Physical Basis for Biological Morphogenesis"

  • Presenter: L Mahadevan, Harvard University
  • Host: Leo Radzihovsky
  • Abstract: The range of shapes in the plant (and animal) world is "enough to drive even the sanest man mad", wrote Darwin. Motivated by qualitative and quantitative biological observations, I will show that there is a "method in the madness" - using examples of growth and form in cells, tissues and organs such as a freely growing pollen tube, undulating fringes on a leaf or petal, the growth of floral spurs, the looping of the gut and the coiling of tendrils. In each case, we will see how a combination of biological and physical experiments, mathematical models and computations allow us to unravel the quantitative basis for the diversity and complexity of biological form, with tantalizing links to evolutionary canalization, biomimetic technologies, and new aspects of geometry and analysis.

Fall 2011 Colloquium Schedule

Colloquia are Wednesdays at 4:00 p.m. in DUAN G1B20, unless otherwise noted.

Coffee, tea and cookies will be available before regular colloquia beginning at 3:45 p.m. in DUAN G1B31.

August 24 — "First Galaxies, First Stars, and the Reionization Epochs of H and He"

  • Presenter: Michael Shull, Astrophysical and Planetary Science, University of Colorado at Boulder
  • Host: Paul Beale
  • Abstract: The universe is thought to have originated in a hot fireball (Big Bang) whose expansion in the presence of dark matter and baryons led to cooling, formation of large-scale structure, the "Dark Ages", and eventually to the first stars and galaxies. I will describe theoretical studies of the expectations for the earliest light in the universe, and the impact of these first galaxies on the high-redshift intergalactic medium. I will then discuss the remarkable new observations by the Hubble Space Telescope of high-redshift galaxies and quasars that probe the predicted epochs of reionization of hydrogen (at a redshift factor z = 7) and singly-ionized helium (at redshift z = 3). We are now learning that the universe was teeming with star-formation activity during its first 500 Myr of existence.

August 31 — "Nonlinear Waves: What You Wanted to Know but..."

  • Presenter: Mark Ablowitz, Applied Math, University of Colorado at Boulder
  • Host: Leo Radzihovsky
  • Abstract: The study of localized waves has a long history dating back to the discoveries in the 1800s describing water waves in shallow water. In fluid dynamics and nonlinear optics there has been considerable interest in various aspects of localized waves. Perhaps surprisingly, nonlinear waves in water and optics have many similar features. After some introductory and historical remarks, topics that will be briefly discussed include: a novel formulation of classical water waves, some new properties of gravity-capillary waves, ultra-short pulse dynamics in mode-locked lasers and nonlinear waves in `photonic graphene'.

September 7 — "The Biology, Chemistry & Physics of RNA Nano-machines"

  • Presenter: Tom Cech, MCDB, University of Colorado at Boulder Director, Colorado Initiative in Molecular Biotechnology Nobel Laureate (Chemistry, 1989)
  • Host: Paul Beale
  • Abstract: In this colloquium geared for physicists, Prof. Cech will review the fundamental information flow in biology (DNA --> RNA --> Protein) and tell the story of the discovery of catalytic RNA. He will explain how X-ray crystallography has been used to determine atomic structures of catalytic RNA molecules. He will then move to studies of the RNA-protein machine telomerase, which is required to replicate the very ends of chromosomes. Recent work indicates that the RNA once again plays an active role in catalysis, this time helping to move the telomerase template through the active site of the enzyme.

September 14 — "Unfinished Business in Particle Physics"

  • Presenter: Jonathan Rosner, Physics, University of Chicago
  • Host: Eric Zimmerman
  • Abstract: The past fifty years have seen an incredible consolidation of results in particle physics into a unified picture known as the Standard Model. In one view, only one piece of this puzzle remains - the Higgs boson. I will argue that, on the contrary, we are seeing only the tip of a very large iceberg, with many exciting discoveries to come in the coming decades.

September 21 — "The Light, and Sound, Fantastic: Radiation Pressure at the Nanoscale"

  • Presenter: Oskar Painter, Applied Physics, California Institute of Technology
  • Host: Jun Ye
  • Abstract: In the last several years, rapid advances have been made in the field of cavity optomechanics, in which the usually feeble radiation pressure force of light is used to manipulate, and precisely monitor, mechanical motion.Amongst the many new geometries studied, coupled phononic and photonic crystal structures (dubbed optomechanical crystals) provide a means for creating integrated, chip-scale, optomechanical systems. Applications of these new nano-opto-mechanical systems include all-optically tunable photonics, optically powered RF and microwave oscillators, and precision force/acceleration and mass sensing. Additionally there is the potential for these systems to be used in hybrid quantum networks, enabling storage or transfer of quantum information between disparate quantum systems. A prerequisite for such quantum applications is the removal of thermal excitations from the low-frequency mechanical oscillator. In this talk I will describe our recent efforts to optically cool and measure the quantum mechanical ground-state of a GHz oscillator (see figure below), and to demonstrate efficient translation between light and sound quanta.

September 28 — "Tracing Attosecond Dynamics of Electrons in Molecules"

  • Presenter: Andreas Becker, Physics, JILA
  • Abstract: In the past time-resolved experiments and theoretical analysis explored molecular rotation and vibration as well as chemical reactions on the time scale of atomic motion. Recent advances in laser science led to the development of attosecond laser pulses (1 atomic unit = 24 attoseconds) which can uncover new insights in the inner dynamics of atoms and molecules on the natural time scale of electronic motion. In my talk I will present physical concepts behind attosecond laser technology and my perspective on the current status of attosecond science. I will then discuss ongoing theoretical and experimental efforts to monitor and control the dynamics of an electron in the chemical bond of a molecule, using nature's most simplest molecule as an example.

October 5 — "Flight of the Fruit Fly: Life at Intermediate Reynolds Numbers"

  • Presenter: Itai Cohen, Physics, Cornell University
  • Host: Leo Radzihovsky
  • Abstract: There comes a time in each of our lives where we grab a thick section of the morning paper, roll it up and set off to do battle with one of nature's most accomplished aviators - the fly. If however, instead of swatting we could magnify our view and experience the world in slow motion we would be privy to a world-class ballet full of graceful figure-eight wing strokes, effortless pirouettes, and astonishing acrobatics. After watching such a magnificent display, who among us could destroy this virtuoso? How do flies produce acrobatic maneuvers with such precision? What control mechanisms do they need to maneuver? More abstractly, what problem are they solving as they fly? Despite pioneering studies of flight control in tethered insects, robotic wing experiments, and fluid dynamics simulations that have revealed basic mechanisms for unsteady force generation during steady flight, the answers to these questions remain elusive. In this talk I will discuss our strategy for investigating these unanswered questions. I will begin by describing our automated apparatus for recording the free flight of fruit flies and a new technique called Hull Reconstruction Motion Tracking (HRMT) for backing out the wing and body kinematics. I will then show that these techniques can be used to reveal the underlying mechanisms for flight maneuvers, wing actuation, and flight stability. Finally, I will comment on the implications of these discoveries for investigations aimed at elucidating the evolution of flight.

October 12 — "Controlling Molecular Interactions with Electric Fields"

  • Presenter: Heather Lewandowski, Physics, JILA, University of Colorado
  • Abstract: The process of breaking one chemical bond and forming another is challenging to understand at a quantum mechanical level. This basic understanding is important to any molecular reaction. However, the complicated quantum nature of these processes is difficult to explore experimentally because full control over all degrees of freedom is required. In particular, controlling interactions between cold molecules using external electric and magnetic fields can elucidate the detailed role of quantum mechanics in molecular collisions.
    We introduce a versatile platform for investigating atom-molecule interactions at temperatures of 100 mK and demonstrate that an electric field can strongly affect cold atom-molecule collisions. These results show that even when only one of the colliding species is polar, electric fields can have a major effect on the collision dynamics at millikelvin temperatures. These experiments represent a launching pad to understanding and controlling cold chemical reactions.

October 13 (NOTE: Thursday colloquium, different location) — "Revisiting Blackbody Radiation at the Nanoscale"

  • Presenter: Jean-Jacques Greffet, Laboratoire Charles Fabry, Institut d'Optique, CNRS
  • Location: JILA Auditorium
  • Host: Markus Raschke
  • Abstract: When reducing the size of systems down to the nanoscale, usual macroscopic laws are often no longer valid. In this talk, we will show that blackbody radiation is dramatically modified at the nanoscale. We will show that blackbody radiation can be coherent in the near field. We will also show that the energy flux can be orders of magnitude larger than the standard Stefan-Boltzman σT4 law. All these effects cannot be understood in the framework of radiometry. We will briefly discuss how thermal radiation can be described using an electrodynamics framework.

October 19 — "Results from the CMS Experiment at the LHC"

  • Presenter: Kevin Stenson, University of Colorado at Boulder
  • Abstract: The Large Hadron Collider has been colliding protons at a world-record energy of 7 TeV for 18 months. The data collected by the four LHC experiments has expanded our understanding of the most fundamental forces of nature. Following a description of the accelerator and experiment, I will present a selection of results from the CMS experiment. These results include searches for the Higgs boson and for new physics such as supersymmetry. I will also provide an outlook of the physics still to come from the LHC as the luminosity and energy increase.

October 26 — "What if we don't find the Higgs?"

  • Presenter: Adam Martin, Fermilab
  • Host: Anna Hasenfratz
  • Abstract: With the first full year of LHC running nearly over, the Higgs boson has yet to be seen. While there are a few places left where it can hide, they are getting fewer by the day. In this talk I will review the role the Higgs boson plays in the standard model and discuss how the theory can be adjusted to 'hide' the Higgs. These adjustments range from slight tweaks to the Higgs decay channels to removing the Higgs boson completely!

October 31 (Special Physics Colloquium) — "A Multi-disciplinary Discussion of the CNGS/OPERA Neutrino Speed Anomaly

  • Presenters: Alysia Marino, Eric Zimmerman, Neil Ashby, Judah Levine, Physics, University of Colorado Boulder
  • Abstract: The apparent greater-than-c speed of neutrinos between the CERN accelerator and LGNS OPERA detector at Gran Sasso in Italy is the subject of enormous interest and attention in the scientific community as well as in the media. This seminar will discuss how the measurements were made, concepts of world-wide clock synchronization using GPS coordinate time, and the details of the time difference measurements made in the experiment.

November 2 — "Three-Dimensional Magnetic Field Line Reconnection"

  • Presenter: Walter Gekelman, Physics, UCLA
  • Host: Tobin Munsat
  • Abstract: Magnetic field line reconnection is a processes in which magnetic field energy is converted to particle energy and heating accompanied by changes in the magnetic field topology. It occurs near the surface of the sun and is thought to be responsible for coronal heating. Images and data from the sun and several laboratory experiments indicate that reconnection is a fully three-dimensional process. Reconnection events often involve complex structures called magnetic flux ropes, which are helical magnetic fields with pitch that varies with radius. We describe experiments in the 17-meter long large plasma device (LAPD) at UCLA in which up to three magnetic flux ropes are generated from adjacent pulsed current channels. The flux ropes exert mutual magnetic forces causing them to twist about each other and merge, while the currents associated with the ropes exhibit dynamic behavior and break up into filaments following the merging process. Volumetric space-time data show multiple reconnection sites with time-dependent locations. We describe the concept of the quasi-separatrix layer, a tool to understand and visualize how magnetic field lines reconnect in 3D, observed for the first time in our laboratory. Its three dimensional development will be shown in movies made from the data. Other phenomena such as merging of current sheets leading to filamentation will also be presented.
  • View the presentation slides (pdf).
Experimental data showing selected field lines associated with three flux ropes shown in red, green and blue. The associated currents are yellow. The volumetric data was acquired at 20,000 locations in the LAPD in a box 10m long and 24 cm in the x,y (transverse to B_z) direction. The currents are calculated from ∇× B.

November 9 — "Pairing in Unusual Places — Stretching the Realm of Superconductivity"

  • Presenter: Randall Hulet, Physics, Rice University
  • Host: Leo Radzihovsky
  • Abstract: Ultracold atoms are powerful tools for the investigation of complex many-body phenomena. This is partly a consequence of the ability to vary parameters such as interaction strength and dimensionality. I will discuss experiments on the pairing of spin-polarized 6Li atoms in both 3D and 1D geometries. Spin-polarization of ultracold atoms is accomplished by creating an imbalanced population of two hyperfine levels, a scenario with direct correspondence to magnetized superconductors, and perhaps with the physics of neutron stars. Spin-polarized ultracold atomic gases are excellent candidates for creating the elusive Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) modulated superfluid state, which is characterized by pairs with non-zero center of mass momentum.

November 16 — "Physics Education Research: A Resource for Educational Transformation at a Critical Time"

  • Presenter: Noah Finkelstein, University of Colorado Boulder
  • Abstract: After decades of research into student learning, assessments, and curriculum design, physics is considered one of the leading fields engaged in discipline-based educational research (DBER). Simultaneously, unprecedented national attention is now being paid to the outcomes of and needs for DBER. After framing the national scale scene of physics education, and how physics education research (PER) is positioned to contribute to the national dialog, I will review the growth of our own program at CU, and particularly my own research that examines several of the critical scales of focus in physics education. This work develops a new theoretical line of inquiry in PER through experimental work on student reasoning in physics at the level of the individual, the course, and the departmental scales. I will present samples of these scales reviewing: novel work on student use of representation and analogy in physics learning, demonstration of the impacts of teaching interpretive themes on student learning of quantum mechanics in our modern physics courses, and conclude with how subtle faculty choices influence something as canonical as clicker use in our introductory physics sequence.
  • View a video of the lecture (part 1 and part 2).

November 23 — Fall Break; No Colloquium

November 30 — "Einstein's Next Test"

  • Presenter: Neil Cornish, Montana State University
  • Host: Peter Bender
  • Abstract: When Einstein was asked how he would have reacted if Eddington's expedition to measure the bending of light by the Sun had conflicted with the predictions of general relativity, he replied "Then I would feel sorry for the dear Lord. The theory is correct anyway." Over the ensuing century Einstein's theory has survived a wide array of precision experimental tests. In the coming decade the detection of gravitational waves will allow us to test dynamical, strong field gravity for the first time, including such basic predictions that gravitational waves propagate at the speed of light and come in two transverse polarizations, and that black holes have event horizons. In the next five years the advanced LIGO-Virgo detectors will be online, and the galactic scale gravitational wave detector formed by an array of milli-second pulsars should also be sensitive enough to make a detection. Next decade we hope to fly some variant of the space based LISA detector. I will describe how these instruments can be used to perform unique tests of Einstein's theory.

December 7 — "Search for the Chimera" NOTE LOCATION CHANGE: DUAN G1B30

  • Presenter: James Randi, James Randi Educational Foundation
  • Host: Leo Radzihovsky
  • Abstract: James Randi exposes popularly-accepted fakery by discussing with his audience everything from ESP to dowsing, from academic frauds to faith healers. Randi reveals what really took place in the last three decades in the labs of various prestigious "think tanks" that verified a series of simple magicians tricks as genuine miracles, thus launching a world-wide plague of misinformation, the repercussions of which can still be felt today. This unique and provocative lecture is not only educational but also highly entertaining. It attracts persons of all educational and social backgrounds and provides a rational perspective on the seemingly paranormal and otherwise unexplained happenings in our day-to-day life.

For more information about colloquia this semester, contact: Leo Radzihovsky