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 30 — "What are Saturn’s rings made of?"

• Presenter: Sascha Kempf, University of Colorado, Boulder
• Host:
• Abstract: When Galileo Galilei discovered Saturn’s rings 450 years ago he didn’t even know that he had observed rings. It was Christiaan Huygens who proposed that Saturn is surrounded by a thin solid ring - made of metal. Earth-based spectroscopic observations in 1970 revealed that the rings in fact consist of 95% clean water ice, but the nature of the other 5% of embedded material, which gives the rings their unique reddish tint, is still unknown. It is, however, this little amount of unknown material that will bring us closer to understanding the rings’ origin and provide valuable information about the formation of the Saturnian system as a whole.

After almost 20 years in space, NASA's Cassini spacecraft has begun the final chapter of its remarkable story of exploration: its Grand Finale. Before the spacecraft plunges into Saturn’s atmosphere Cassini is undertaking a daring set of orbits that is, in many ways, a whole new mission. Starting in late April this year Cassini is performing weekly dives between the planet and the inner rim of Saturn’s rings. No other mission has ever explored this region that has been considered until a few years ago to be inaccessible for space probes. Those unique orbits allowed the Cosmic Dust Analyzer (CDA) on Cassini for the very first time to collect material originating from the main rings itself and to identify their composition.

In my talk, I will report about the exciting findings by CDA during Cassini’s swan song.

### September 6 — "Generation and detection of tunable orbital angular momentum in polarization-maintaining optical fiber"

• Presenter: Juliet Gopinath, University of Colorado, Boulder
• Host: John Price
• Abstract: In the past few years, twisted light, or light with orbital angular momentum (OAM) has captured interest a diverse array of applications. It can be used to drive micromachines and in biophotonics, OAM is used in microscopy to achieve resolution orders of magnitude better than the diffraction limit. In astronomy, the OAM of light from distant stars carries information about the inhomogeneity of the interstellar medium and the shape of black holes. In quantum information science, OAM states can be entangled, which leads to surprising demonstrations of quantum mechanics and potentially new computational possibilities. OAM-enabled communications, of all the applications, has received the majority of the attention due to the potential increase in fiber optic bandwidth that would be realized in a move from binary to a classical or quantum mechanical-vast parameter space per photon provided by the integer OAM states.

To date, specialty fiber has been used to carry OAM. In this talk, I will describe new methods for generating OAM light in commercially available polarization maintaining optical fiber. By adding up two higher order modes, generation of tunable OAM can be demonstrated. In addition, I will discuss a new quantitative detection method for light with OAM and extensions of the technique. Finally, I will present a method to control independently, both the OAM and the spatial beam profile.

Biography: Juliet Gopinath is an Associate Professor of Electrical, Computer and Energy Engineering at the University of Colorado Boulder. She received her B.S. degree in Electrical Engineering from the University of Minnesota and her M.S. and Ph.D. degrees at MIT. She worked at MIT Lincoln Laboratory from 2005 to 2009 on topics including cryogenic Yb:YAG lasers, beam combining, and mode-locked diode lasers. Since 2009, she has run a group focused on optical devices and lasers at CU Boulder. Her current research interests include ultrafast lasers, nonlinear optics, mid-infrared materials, spectroscopy, orbital angular momentum and adaptive optical devices. She is the recipient of an Air Force Young Investigator Award (2010), R & D 100 Award (2012), an NSF CAREER award (2016), the CU Provost Achievement Award (2016) and is an Associate Editor for IEEE Photonics Journal.

### September 13 — "Enabling Technology Innovation through Plasma Modeling: Sustainability and Biotechnology as the Next Frontiers"

• Presenter: Mark Kushner, University of Michigan
• Host: John Cary
• Abstract: The field of low temperature plasmas (LTPs) has provided enabling sciences and technologies that are arguably responsible for huge swaths of our industrial and high technology infrastructure.  The information technology revolution has been singularly enabled by the ability to fabricate microchips using LTPs.  Virtually every human implant is fabricated or made biocompatible using LTPs.  All non-incandescent lighting sources rely on LTPs, either directly as the source of photons or indirectly through materials fabrication.  The current generation of jet engines are enabled by LTP processing, and interplanetary missions are made possible by LTP propulsion.  Now, LTPs have the potential to treat wounds and disease, and to convert green-house gases to high value chemicals.  Many of these advances are the end result of scientifically and experimentally inspired technology development, and in some cases incremental advances over many years, with little input from modeling.  The plasma chemistry and plasma surface interactions that are responsible for these successes have untold complexity that acutely challenge diagnostics and modeling, as well as the underlying AMO (atomic, molecular, optical) physics knowledge base.  A legitimate question is – has modeling and simulation been significantly influential in the development of LTP enabled technologies?  Are modeling and simulation LTPs capable of leading innovation?  In this talk, the role and potential of modeling and simulation in the LTP innovation chain will be reviewed with examples from materials processing and the next frontiers of biotechnology and sustainability.  Examples of where modeling has provided insights that stimulated, if not enabled, technology development will be discussed.

### September 20 — "ColdQuanta Incorporated: The History and Future of a University Spinoff Company*"

• Presenter: Dana Anderson, JILA, University of Colorado, Boulder
• Host: John Price
• Abstract: ColdQuanta Inc. was founded in 2007 by three physicists and a businessman, myself, Theodor Hänsch, Jakob Reichel and Rainer Kunz.  Its mission is to develop and commercialize cold and ultracold matter technology that can enable the scientific and applications communities.  Much of ColdQuanta’s early technology emerged from a MURI grant from the Army Research Office and more so, a large DARPA grant to develop technology for guided Bose-Einstein Condensate (BEC) applications. Out of that effort came compact components for producing ultracold matter and in particular a sophisticated “atom chip” technology that made it possible to considerably reduce the size of BEC machines and similar systems.  A BEC machine that in the past took many months to build, occupied a large optical table and needed racks of electronic instrumentation can now be purchased from ColdQuanta, occupies a single rack, and can be up and running in six hours.  Since 2007 ColdQuanta has produced instruments for making cold atoms in undergraduate labs, and has enabled numerous applications and scientific experiments from optical lattices to quantum computing to the JPL/NASA mission to put cold atoms on the International Space Station.  This talk tells the story of how ColdQuanta was formed and highlights the role of students and spin-off companies in the University’s mission to provide an educated workforce, to promote scientific advancement, and to maintain this nation’s technological leadership.  It also covers some relevant “this is reality” topics such as starting a tech business, money, and conflicts of interest.  Regarding the latter:

*I hereby disclose that I have a financial interest in ColdQuanta, Inc. (!)

### September 27 — "The Quest for the New Standard Model: Searching for BSM Physics with Rare-Isotope Beams"

• Presenter: Kyle Leach, Colorado School of Mines
• Host: Eric Zimmerman
• Abstract: The development of the Standard Model (SM) has been one of the crowning achievements in modern physics, and is the cornerstone of current subatomic studies. Despite its success, the SM is known to be incomplete, and providing limits on possible physics beyond the Standard Model (BSM) is crucial to our understanding of the natural universe.  Although they are generally complex, atomic nuclei can be exploited as a laboratory for these studies through the use of rare-isotope beams (RIBs).  The production of these short-lived, very exotic isotopes has opened new avenues of research in our search for BSM physics in the era of the LHC.  This work is at the precision and sensitivity frontiers, and helps to bridge the gap between atomic, nuclear, and particle physics using novel, state-of-the-art detection techniques. In this talk, I will use these topics to highlight the significant role of the atomic nucleus in our ongoing search for additional generations of quarks, new descriptions of the weak interaction, and light dark matter. These studies play a critical role in providing the groundwork for our quest to develop the "New Standard Model".

### October 4 — "Broadening the Searchlight: New Ideas in Dark Matter Detection"

• Presenter: Kathryn Zurek, LBNL
• Host: Ethan Neil
• Abstract: Searches for massive dark matter have largely focused on a mass window near the weak scale, the so-called "WIMP window". This window is, however, becoming increasingly closed by both the LHC and the unprecedented sensitivity of direct detection experiments. At the same time, theoretical work in recent years has shown lighter dark matter candidates in a hidden sector are theoretically well-motivated, natural and arise generically in many theories beyond the standard model. New ideas are needed to search for dark matter with mass below a GeV and as light as the warm dark matter limit of a keV. We propose new ideas to search for such light dark matter with superconductors, semi-conductors, graphene, Dirac materials, and superfluid helium. We show that these same experiments, through inelastic processes, may also be sensitive to dark matter with masses in the meV to keV mass window, broadening the mass reach to light dark matter by many orders of magnitude.

### October 11 — "Spin Orbit Coupled Quantum Magnetism"

• Presenter: Kate Ross, Colorado State University
• Host: Chuck Rogers
• Abstract: Strong quantum fluctuations and spin entanglement can lead to exotic emergent many body properties of materials, such as fractionalized excitations predicted for quantum spin liquids, or the field-tuned Bose Einstein Condensation observed in quantum dimer crystals.  Traditionally, the materials space in which these types of phases are sought has been limited to materials with “pure" spin 1/2, as obtainable from Cu2+ for instance, and most theories have therefore focused on the isotropic exchange limit.  However, attention has recently shifted towards quantum materials in which an interplay of strong spin orbit coupling and crystal electric field effects lead to a "pseudo-spin" 1/2.  The magnetic interactions in these materials can be described by anisotropic effective exchange models, which can lead to new predicted quantum many body phenomena such as the Majorana fermion excitations of Kitaev quantum spin liquid, or emergent electrodynamics in quantum spin ice.  I will discuss some recent material examples that exemplify this new paradigm.

### October 18 — "The Remarkable Ways in Which Gases Dissolve and React in Water"

• Presenter: Gilbert Nathanson, Department of Chemistry, University of Wisconsin, Madison
• Host: David Nesbitt
• Abstract: Interfacial reactions between atmospheric gases and sea spray play a vital role in our air quality and climate.  These reactions also display fascinating dynamics at the atomic scale.  From this microscopic perspective, the interfacial encounter begins when gas molecules strike the surface of an aqueous solution that might contain ions and biological molecules.  We rely on understanding the physics of these gas-liquid collisions to construct a “blow-by-blow” picture of the solvation and reaction of acids, bases, and oxidizers in such complex solutions.  I will describe experiments using microjets and coated wheels that enable us to explore sea-spray mimics inside a vacuum chamber and help reveal how aerosol-mediated reactions takes place.

### October 25 — "Generation and Application of Attosecond Laser Pulses"

• Presenter: Andreas Becker, JILA, University of Colorado, Boulder
• Host: John Price
• Abstract: High harmonic generation provides a unique technique to generate coherent light up to keV photon energies, which is emitted in pulses a few tens of attoseconds in duration. Such pulses can now be used to probe dynamics in matter on the time scale of electronic motion. I will present our theoretical efforts to perform numerical calculations capturing the highly nonlinear process of attosecond pulse generation on both the microscopic level of a single atom and the macroscopic level of the generating gas medium consisting of billions of atoms. In the second part I will then discuss examples of the application of attosecond pulses to resolve electron dynamics in atoms and molecules.

### November 1 — "Transient Crosslinkers Tune the Patterns of Microtubule Filaments"

• Presenter: Jennifer Ross, University of Massachusetts, Amherst
• Host: Meredith Betterton
• Abstract: The cell is a complex autonomous machine taking in information, performing computations, and responding to the environment. To enable agile read/write capabilities, much of the molecular biochemistry that performs these computations must be transient and weak, allowing signals to be carried as a function of the concentration of numerous and coupled interactions. Traditionally, biochemical experiments can only measure strongly interacting systems that can last for long times in dilute concentrations. We have developed microscopy measurements to enable to visualization of weak, transient interactions and the resulting emergent behaviors of coupled systems. I will present excerpts from stories where many weak, transient interactions can have strong repercussions on the overall activity and can, in fact, overpower strongly interacting systems. These studies involve the microtubule cytoskeleton and the transport motor, kinesin-1.  Our results reveal a fundamentally important aspect of cellular self-organization: weak, transient interacting species can tune their interaction strength directly by tuning the local concentration to act like a rheostat. The tunability of weak, transient interactions is a fundamental activity of biological systems, and our insights will ultimately enable us to learn how to engineer these systems to create biological or biomimetic devices.

Biography: Ross is the director of the new Massachusetts Center for Autonomous Materials (MassCAM) and an award-winning biophysicist studying the organization of the microtubule cytoskeleton and microtubule-based enzymes using high-resolution single molecule imaging techniques. She has a degree in Physics and has studied the microtubule cytoskeleton for over a decade. As a Cottrell Scholar, Ross has pioneered innovative teaching techniques that are being adopted around the world. Specifically, she has taught at several international short courses on microscopy including Analytical and Quantitative Microscopy (AQLM) at the Marine Biology Laboratory and the Bangalore Microscopy Course at the National Centre for Biological Science in Bangalore, India. She has also served as the President of NESM in the past. She is also an advocate for women and under-represented groups and has a blog to help others make it in academics.

### November 8 — "Tests of quantum mechanics and gravitation with atom interferometry"

• Presenter: Mark Kasevich, Stanford University
• Host: Scott Diddams
• Abstract: Recent de Broglie wave interference experiments with atoms have achieved wavepacket separations as large as 54 cm over time intervals of 2 sec. These experiments, and their impact on gravitational and quantum physics, will be discussed.

### November 29 — "What's Next in Higgs Physics?"

• Presenter: Sridhara Dasu, University of Wisconsin
• Host: Bill Ford
• Abstract: The discovery of the Higgs boson in 2012 by the LHC experiments, ATLAS and CMS, was celebrated enthusiastically by the world. The new datasets from 2015-16 have solidified that discovery, further establishing the H(125 GeV) to be Standard Model (SM)-like. Nevertheless, explorations of the Higgs sector beyond the SM are important, as they often involve additional scalar and pseudo-scalar particles. We are making significant headway in mapping out the details of the Higgs sector already, searching for heavier Higgs bosons and rare decays of the H(125). This scalar Higgs sector could also be a portal to the "dark" sector, which we know little about from particle physics point of view. This talk will discuss the latest status of the CMS Higgs sector exploration.
Further exploration of Higgs sector is promising, but is experimentally challenging, due to low energies of the Higgs decay products.
Implications for future improvements needed for the experimental facilities will also be briefly discussed.

### December 6 — "From simple to complex atoms for atomic qubits and scalable quantum computing"

• Presenter: Mark Saffman, University of Wisconsin
• Host: Dana Anderson
• Abstract: Quantum computing is a few decades old and is currently an area where there is great excitement and rapid developments. A handful of distinct approaches have shown the capability of on-demand generation of entanglement and execution of basic quantum algorithms.
One of the daunting challenges in developing a quantum computer is the need for a very large number of qubits. Neutral atoms are one of the most promising approaches for meeting this challenge. I will give a snapshot of the current status of atomic quantum computing, describe the physics underlying neutral atom qubits and quantum gates, and show how one of the most complicated atoms in the periodic table may lead to some simple solutions to hard problems.
• Bio: Mark Saffman is an experimental physicist working in the areas of atomic physics, quantum and nonlinear optics, and quantum information processing. He has made significant contributions to the physics of optical solitons, pattern formation, sources of entangled light, and quantum computing. His current research effort is devoted to the development of neutral atom based quantum computing devices. His research team was the first to demonstrate a quantum CNOT gate between two trapped neutral atoms, and the deterministic entanglement of a pair of neutral atoms. This was done using dipole mediated interactions between highly excited Rydberg atoms. He is currently developing scalable neutral atom platforms using arrays of trapped atoms.
He is a Professor of Physics at the University of Wisconsin-Madison, and a fellow of the American Physical Society and the Optical Society of America. He has been recognized with the Alfred P. Sloan Fellowship and a University of Wisconsin Vilas Associate Award. He also serves as an Associate Editor for Physical Review A.

### December 13 — "First Results from CUORE: Majorana Neutrinos and the Search for Neutrinoless Double-Beta Decay"

• Presenter: Lindley Winslow, MIT
• Host: Alysia Marino
• Abstract: The neutrino is unique among the Standard Model particles. It is the only fundamental fermion that could be its own antiparticle, a Majorana particle. A Majorana neutrino would acquire mass in a fundamentally different way than the other particles and this would have profound consequences to particle physics and cosmology. The only feasible experiments to determine the Majorana nature of the neutrino are searches for the rare nuclear process neutrinoless double-beta decay.  CUORE uses tellurium dioxide crystals cooled to 10 mK to search for this rare process.  In this talk, I will present the first results from this detector and highlight my group’s R&D efforts and our other efforts including axions and nanoparticle-based liquid scintillators.

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.

### 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 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.

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"

• Presenter: 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.

### September 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.

### October 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

### 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
• 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
• 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.

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

• Presenter: Steve Girvin, Yale
• 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
• 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
• 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
• 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
• 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
• 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?"

• 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).

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

• Presenter: Randall Hulet, Physics, Rice University
• 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 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