Colloquia are Wednesdays at 9:00 a.m. unless otherwise noted and will be presented online via zoom. All meetings are password protected. If you are not a student/faculty member in physics, pre-register with Veronica Lingo to attend a lecture.
January 13 — "The Mechanics of Non-Equilibrium Soft Interfaces"
- Presenter: Michael Murrell, Yale University
- Host: Loren Hough
- Abstract: At small length-scales, capillary effects are significant, and thus the mechanics of soft material interfaces may be dominated by solid surface stresses and liquid surface tensions. The balance between surface and bulk properties is described by an elasto-capillary length-scale, in which equilibrium interfacial energies are constant. However, at small length-scales in biological materials, including living cells and tissues, interfacial energies are not constant, but are actively regulated and driven far from equilibrium. Thus, the balance between surface and bulk properties depends upon the distance from equilibrium, defining a novel material parameter, what we term “active” elasto-capillarity. Here, we model the adhesion and spreading (wetting) of living cell aggregates as ‘active droplets’, with a non-equilibrium surface energy that depends upon internal stress generated by the actomyosin cytoskeleton. Depending upon the extent of activity, the droplet may exhibit both surface stress and surface tension, and each may adapt to the mechanics of their surroundings. The impact of this activity-dependent adaptation challenges contemporary models of interfacial mechanics, including traditional and extensively used models of contact mechanics and wetting. Finally, we show the origin of adaptation is in the breaking of detailed balance at the molecular scale by stochastic binding in the actomyosin cytoskeleton.
January 20 — "Nature’s optics and our understanding of light"
- Presenter: Sir Michael Berry, University of Bristol
- Host: Rahul Nandkishore
- PLEASE NOTE SPECIAL TIME: 4:00 p.m.
- Abstract: Optical phenomena visible to everyone have been central to the development of, and abundantly illustrate, important concepts in science and mathematics. The phenomena considered include rainbows, sparkling reflections on water, green flashes, earthlight on the moon, glories, daylight, crystals, and the squint moon. The concepts include refraction, caustics (focal singularities of ray optics), wave interference, numerical experiments, mathematical asymptotics, dispersion, complex angular momentum (Regge poles), polarization singularities, Hamilton’s conical intersections of eigenvalues (‘Dirac points’), geometric phases, and visual illusions.
January 27 - No Colloquium
February 3 — "Towards quantitative theories of correlated electron materials"
- Presenter: Garnet Chan, California Institute of Technology
- Host: Rahul Nandkishore
- Abstract: I will talk about two topics. In the first part, I will discuss our efforts in the last decade to elevate the understanding of correlated materials from the level of lattice models to atomistic level details and quantitative precision. In the second part, I will describe a current, partially completed, program of research to build a unified numerical machinery to model realistic many-particle and many-electron problems based on tensor networks.
February 10 — "The XYZ Affair: Tales of the Third (and Fourth) Hadrons"
- Presenter: Richard Lebed, Arizona State University
- Host: Tom DeGrand
- Abstract: In the past two decades, many new particles have been discovered that are clearly hadrons (interacting via the strong nuclear force through the theory called QCD), but do not seem to fit into either of the known hadron categories of meson (quark-antiquark) or baryon (3 quarks). Several species of these “exotic” particles, called X, Y, and Z, are now believed to be tetraquarks, and in July, 2015 researchers at the Large Hadron Collider announced the discovery of pentaquark states, P_c. We begin by reviewing the basics of QCD (quarks, color, confinement, etc.), and then turn to the question of how conventional mesons are identified, which allows one to distinguish exotics. After reviewing their experimental discovery, we consider the question of how exotics are assembled. Several competing physical pictures attempt to describe the structure of exotics: as molecules of known hadrons, as the result of kinematical effects, and others. I propose that at least some of them arise due to the formation of compact diquarks, a well-known but under-appreciated phenomenon of QCD. The competing facts of kinematics and diquark confinement create an entirely new kind of bound state: not a molecule with well-defined orbits, but an extended object that lasts only as long as it takes for quantum mechanics to allow the separated quarks and antiquarks to “find” one another, and allow decays to occur. I will discuss several observed effects that support this picture.
February 17 — "How behavioral and evolutionary constraints sculpt early visual processing"
- Presenter: Stephanie Palmer, University of Chicago
- Host: Loren Hough
- Abstract: An animal eye is only as efficient as the organism’s behavioral constraints demand it to be. While efficient coding has been a successful organizational principle in vision, to make a more general theory, behavioral, mechanistic, and even evolutionary constraints need to be added to this framework. In our work, we use a mix of known computational hurdles and detailed behavioral measurements to add constraints to the notion of optimality in vision. Accurate visual prediction is one such constraint. Prediction is essential for interacting fluidly and accurately with our environment because of the delays inherent to all brain circuits. In order to interact appropriately with a changing environment, the brain must respond not only to the current state of sensory inputs but must also make rapid predictions of the future. In our work, we explore how our visual system makes these predictions, starting as early as the eye. We borrow techniques from statistical physics and information processing to assess how we get terrific, predictive vision from these imperfect (lagged and noisy) component parts. To test whether the visual system performs optimal predictive compression and computation, we compute the past and future stimulus information in populations of retinal ganglion cells, and in the vertical motion sensing system of the fly. In the fly, we anchor our calculations with careful measurements from the Dickinson group on fast evasive flight maneuvers. This survival-critical behavior requires fast and accurate control of flight, which we show can be achieved by visual prediction in the fly vertical sensing system, via a specific wiring motif. Moving on from behavior, developing a general theory of the evolution of computation is a current research direction in our group. We use the repeated evolution of tetra-chromatic color vision in butterflies to test hypotheses about whether neural computations contain shadows of the evolutionary history of the organism.
**SPECIAL Physics/RASEI Colloquium** February 17 — "Metal halide perovskites: an introduction to hybrid semiconductors"
- Presenter: Joseph Berry, NREL
- Host: Michael Ritzwoller
- PLEASE NOTE SPECIAL TIME: 4:00 p.m.
- Abstract: Over the past decade metal halide perovskites (MHPs) have emerged as potentially transformational materials for enabling low-cost high efficiency photovoltaics (PVs). In the time since the initial reports of PV based on these materials, current state-of-the-art devices have reached lab scale solar cell efficiencies exceeding any other polycrystalline thin film technology. In addition, MHPs have shown the promise of creating low-cost high efficiency tandems based on both all-perovskite configurations and in combination with incumbent technologies (i.e., Si, CIGS) to target performance beyond single junction PV efficiency limits. This colloquium will provide an introduction to these materials and their physical properties that have made them truly unique as PV absorbers. Current topics in PV research will be touched upon to indicate some of the motivations for a larger exploration of hybrid organic-inorganic semiconductors more generally. Selected work in this broader class of hybrid materials will be presented to provide a perspective on the opportunities they offer. Finally, some outstanding questions regarding how to understand and ultimately manipulate some of the more unique behaviors of these materials will also be highlighted.
February 24 — "Radio Astrophysics from the Moon"
- Presenter: Jack O Burns, CASA, University of Colorado, Boulder
- Host: Michael Ritzwoller
- Abstract: A new era of exploration of the low radio frequency Universe from the Moon will soon be underway with landed payload missions facilitated by NASA’s Commercial Lunar Payload Services (CLPS) program. CLPS landers are scheduled to deliver two radio science experiments, ROLSES to the nearside and LuSEE to the farside, beginning later this year. These instruments will be pathfinders for a 21-cm Global Signal Cosmology telescope (DAPPER) and a 10-km diameter interferometric array, FARSIDE, composed of 128 pairs of dipole antennas. ROLSES and LuSEE, operating at frequencies from ~100 kHz to a few tens of MHz, will investigate the plasma environment above the lunar surface and measure the fidelity of radio spectra on the surface. ROLSES will measure the photoelectron sheath density to better understand the charging of the lunar surface. LuSEE will measure the local magnetic field and exo-ionospheric density, interplanetary radio bursts, and the galactic synchrotron spectrum. DAPPER is designed to open a new window to the cosmos, the Dark Ages and Cosmic Dawn, using the highly redshifted hyperfine line of neutral hydrogen observed from 10-110 MHz. FARSIDE will break new ground by imaging radio emission from Coronal Mass Ejections (CME) beyond two solar radii, and detect auroral radio emission from the magnetic fields of nearby potentially habitable exoplanets.
**SPECIAL Physics/Applied Mathematics Colloquium** February 24 — "Evidence-Based Elections"
- Presenter: Philip Stark, University of California, Berkeley
- Host: Michael Ritzwoller
- NOTE SPECIAL TIME: 4:00 p.m. MST
- Abstract: Elections rely on people, hardware, and software, all of which are fallible and subject to manipulation. Well resourced nation-states continue to attack U.S. elections. Voting equipment is built by private vendors–some foreign, but all using foreign parts. Many states even outsource election results reporting to foreign firms. How can we conduct and check elections in a way that provides evidence that the reported winners really won–despite malfunctions and malfeasance? Evidence-based elections require voter-verified (generally, hand-marked) paper ballots kept demonstrably secure throughout the canvass and manual audits of election results against the trustworthy paper trail. Hand-marked paper ballots are far more trustworthy than machine-marked ballots for a variety of reasons. Two kinds of audits are required to provide affirmative evidence that outcomes are correct: _compliance audits_ to establish whether the paper trail is complete and trustworthy, and _risk-limiting audits_ (RLAs). RLAs test the hypothesis that an accurate manual tabulation of the votes would find that one or more reported winners did not win. To reject that hypothesis means there is convincing evidence that a full hand tally would confirm the reported results. For a broad variety of social choice functions, including plurality, multi-winner plurality, supermajority, proportional representation rules such as D’Hondt, Borda count, approval voting, and instant-runoff voting (aka ranked-choice voting), the hypothesis that one or more outcomes is wrong can be reduced to the hypothesis that the means of one or more lists of nonnegative numbers is not greater than 1/2. Martingale methods for testing such nonparametric hypotheses sequentially are especially practical. RLAs are in law in several states and have been piloted in more than a dozen; there have been roughly 60 pilots in jurisdictions of all sizes, including roughly 10 audits of statewide contests. Open-source software to support RLAs is available.
March 3 — "One-way quantum interactions for fun and profit"
- Presenter: Aashish Clerk, University of Chicago
- Host: Ana Maria Rey
- Abstract: The most common kinds of interactions in physics obey a basic kind of reciprocity: when two systems or particles interact, each one influences the other, and information flows in both directions. In this talk, I’ll discuss general methods for engineering interactions that break this symmetry, in a fully consistent quantum setting. These engineered “one-way” quantum interactions open up a host of unusual possibilities, from new methods for manipulating and processing quantum information, to new kinds of topological and many-body physics. I’ll introduce some of the basic theoretical ideas that underlie these unusual interactions, and connections to recent interest in “non-Hermitian” quantum systems. I’ll also discuss recent experimental implementations in quantum optomechanical systems and superconducting quantum circuits.
March 10 — Adaptability, Thinking, and Inclusion – A not so random walk
- Presenter: Patricia Rankin, University of Colorado, Boulder
- Host: Michael Ritzwoller
- Abstract: Physicists at heart are problem solvers. This talk looks at how a precision measurement of the mass and width of the Z0 required a variety of problem-solving approaches driven by a need to adapt to changing expectations. Next, I will discuss a more general framework for thinking about the types of problems we encounter and ways to approach them. This framework and the need for us to work on grand challenge problems such as climate change motivates the final part of my talk which will discuss the ways we need to reconsider both how we train the students we have and how we approach the recruiting and retention of physicists in general.
March 17 — "Using magnetic fields and microgravity to explore the physics of dusty plasmas"
- Presenter: Ed Thomas, Auburn University
- Host: Mihaly Horanyi
- Abstract: Over the last three decades, plasma scientists have learned how to control a new type of plasma system known as a “complex” or “dusty” plasma. These are four-component plasma systems that consist of electrons, ions, neutral atoms, and charged, solid, nanometer- to micrometer-sized particles. The presence of these microparticles allow us to “tune” the plasma to have solid-like, fluid-like, or gas-like properties. This means that dusty plasmas are not just a fourth state of matter – they can take on the properties of all four states of matter.
- From star-forming regions to planetary rings to fusion experiments, charged microparticles can be found in many naturally occurring and man-made plasma systems. Therefore, understanding the physics of dusty plasmas can provide new insights into a broad range of astrophysical and technological problems. This presentation introduces the physical properties of dusty plasmas – focusing on how the small charge-to-mass ratio of the charged microparticles gives rise to many of the characteristics of the system. In particular, dusty plasmas can be used to study a variety of processes in non-equilibrium or dissipative systems such as self-organization and energy cascade as well as a variety of transport and instability mechanisms. This presentation will discuss results from our studies of dusty plasmas in high (B ≥ 1 T) magnetic fields using the Magnetized Dusty Plasma Experiment (MDPX) device at Auburn University and in microgravity experiments using the Plasmakristall-4 (PK-4) laboratory on the International Space Station.
March 24 — "Creating and measuring the elusive Majorana fermion"
- Presenter: Vidya Madhavan, University of Illinois Urbana-Champaign
- Host: Dan Dessau
- Abstract: In 1937, Ettore Majorana predicted the existence of a special class of fermions where the particle and the anti-particle are identical. However, with the possible exception of neutrinos, there are no known fundamental particles that belong to this class. The possible realization of Majorana fermions as quasiparticle excitations in solids has rekindled interest in these particles, especially since Majorana states in solids may be useful as fault tolerant qubits for quantum information processing. While most studies have focused on Majorana bound states which can serve as topological qubits, more generally, akin to elementary particles, Majorana fermions can propagate and display linear dispersion. This talk is focused on recent work in realizing Majorana modes in condensed matter systems. I will first describe in detail the conditions under which such states can be realized and what their signatures are. I will then show scanning tunneling microscopy data on 1D domain walls and step edges in two different superconductors, which might potentially be the first realizations of dispersing Majorana states in 1D.
March 31 — "On Ising's model of ferromagnetism"
- Presenter: Peter Armitage, Johns Hopkins University
- Host: Rahul Nandkishore
- Abstract: The 1D Ising model is a classical model of great historical significance for both classical and quantum statistical mechanics. Developments in the understanding of the Ising model have fundamentally impacted our knowledge of thermodynamics, critical phenomena, magnetism, conformal quantum field theories, particle physics, and emergence in many-body systems. Despite the theoretical impact of the Ising model there have been very few good 1D realizations of it in actual real material systems. However, it has been pointed out recently, that the material CoNb2O6, has a number of features that may make it the most ideal realization we have of the Ising model in one dimension. In this talk I will discuss the surprisingly complex physics resulting in this simple model and review the history of "Ising's model" from both a scientific AND human perspective. In the modern context I will review recent experiments by my group and others on CoNb2O6. In particular I will show how low frequency light in the THz range gives unique insight into the tremendous zoo of phenomena arising in this simple model system.
April 7 — "A brief history of time crystals"
- Presenter: Shivaji Sondhi, Princeton University
- Host: Rahul Nandkishore
- Abstract: A time crystal should break time translation symmetry in the same sense as a spatial crystal breaks spatial translation symmetry. While this is an intuitively appealing idea, it also runs up against the tendency of macroscopic systems to equilibrate which is why perpetual motion machines are not commonly available. I will discuss the history of this idea and how, in the recent efflorescence of non-equilibrium quantum dynamics a phase with a family resemblance to this idea was discovered. It requires working out of quilibrium, generalizing the idea of a phase and breaking a discrete time translation symmetry - but at the end of it all we have a genuinely new macroscopic and surprisingly robust phenomenon. I will also report on the status of its experimental realization.
April 14 — "Quantum Many-body theory in the Quantum Information era"
- Presenter: Matthew Fisher, University of California, Santa Barbara
- Host: Rahul Nandkishore
- Abstract: Traditionally, quantum many-body theory has focused on ground states and equilibrium properties of spatially extended systems, such as electrons and spins in crystalline solids. In recent years \noisy intermediate scale quantum computers" (NISQ) have emerged, providing new opportunities for controllable non-equilibrium many-body systems. In such dynamical quantum systems the inexorable growth of non-local quantum entanglement is expected, but monitoring such open systems (by making projective measurements) can compete against entanglement growth. In this talk I will describe recent theoretical work exploring the behavior of \hybrid" quantum circuits consisting of both unitary gates and projective measurements. These circuits can be shown to exhibit a novel quantum dynamical phase transition between a weak measurement phase and a quantum Zeno phase. Detailed properties of the weak measurement phase - including relations to quantum error correcting codes - and of the critical properties of this novel quantum entanglement transition will be described.
April 21 — "Element synthesis and neutrinos in neutron star mergers"
- Presenter: Gail McLaughlin, NC State University
- Host: Paul Romatschke
- Abstract: The merging of two neutron stars is a true multimessenger event which includes gravitational waves, an electromagnetic signal and the emission of enormous numbers of neutrinos. In order to understand these signals we need a careful accounting of the microphysics that occurs during and after the merger. I will focus on the elements produced in these objects and the effect of two aspects of this microphysics; nuclear models/reactions and neutrino flavor transformation physics. In particular, I will discuss the importance of new developments in these areas to predictions of kilonova light curves and the astrophysical origin of the r-process.
April 28 — "Superconductivity in the Hubbard Model"
- Presenter: Steve Kivelson, Stanford University
- Host: Rahul Nandkishore
- Abstract: A search on Google Scholar for “Hubbard Model” yields a million results! Since the discovery of high temperature superconductivity in the cuprates, much of the discussion concerning the mechanism of superconductivity in these (and other) materials has involved stories about the behavior of this paradigmatic model. Real materials are complicated, with observable behaviors that are sensitive to all sorts of microscopic details, leading to debates over what is essential and what is a herring of one color or another. However, as will be discussed in this talk, some conditions for the existence of superconductivity in the Hubbard model can be addressed clearly, using theoretical tools that are controlled and unambiguous in appropriate limits.
For more information about colloquia this semester, contact: Rahul Nandkishore.
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 — "New frontiers for localization"
- Presenter: Rahul Nandkishore, University of Colorado, Boulder
- Host:
- Abstract: Localization is a central paradigm for non-equilibrium quantum physics. I will explain what localization is, and why it is interesting, highlighting in particular some of the new phases that can arise in the localized regime, which have no equilibrium counterparts. I will then present some of my recent work demonstrating that localization can arise in settings where it was previously believed to be impossible, such as systems with long range interactions. I will conclude with a discussion of some recent developments, their implications, and an outlook for the field.
September 4 — "Breaking Bias"
- Presenter: Stefanie Johnson, Leeds School of Business, University of Colorado, Boulder
- Host: Eric Cornell
- Abstract: In this talk, Johnson explains the biases that impede diversity initiatives and provides ways of overcoming those biases to effectively promote diversity in organizations. She specifically will talk about one example of a diversity intervention at the Hubble Space Telescope. Johnson then covers strategies to interrupt unconscious biases though different cognitive mechanisms.
September 11 — "In search of new scales of compositeness"
- Presenter: Ethan Neil, University of Colorado, Boulder
- Host:
- Abstract: The study of particle physics has a long history of uncovering compositeness - new substructures within particles that were at first believed to be fundamental. Are the current set of "fundamental" particles contained in the Standard Model hiding even smaller structures? In this talk, I will explore the physics of composite particles, the current state of experimental searches for compositeness, and distinctive signatures of undiscovered strongly-coupled composite particles such as composite dark matter.
September 18 — "New Detectors for Probing Our Universe"
- Presenter: Peter Graham, Stanford University
- Host: James K. Thompson
- Abstract: High precision technology offers a powerful new approach for particle physics and cosmology. In recent years there has been a surge of interest in using technologies such as atom interferometry, nuclear magnetic resonance, and high precision magnetometry in addition to the more traditional particle detection techniques. Excitingly, such technologies can allow the discovery of new physics which is otherwise completely undetectable by conventional techniques. For example the axion is one of the most strongly-motivated dark matter candidates, however to date only a small fraction of its parameter space has been explored. I will discuss several new experimental approaches to searching for this type of “ultralight” dark matter. Interestingly, these approaches are similar in many respects to gravitational wave detection. I will also discuss the use of atom interferometry for gravitational wave and dark matter detection and the new MAGIS detector. Such precision experiments will open new avenues for probing the origin and composition of the universe.
September 25 — "Disorder as a driver of biological filtration"
- Presenter: Loren Hough, University of Colorado, Boulder
- Abstract: Intrinsically disordered proteins are flexible polymers that play a wide variety of vital cellular roles. Their disruption leads to a wide range of diseases, from cancer to neurodegeneration. Disordered proteins present a fascinating enigma; how they can be so important for cell function while remaining flexible and highly dynamic rather than forming well-defined structures? One role of intrinsically disordered proteins is to form the primary filter of the nuclear pore complex. This remarkable filter allows the selective passage of some macromolecules while inhibiting the passage of others. We combine nuclear magnetic resonance spectroscopy within living cells, bench-top experiments and analytical models to show that binding to flexible filaments can give rise to unexpected diffusive properties that contribute to motion through biological filters.
October 2 — "Network architectures supporting learnability"
- Presenter: Danielle Bassett, University of Pennsylvania
- Host: Loren Hough
- Abstract: Human learners acquire not only disconnected bits of information, but complex interconnected networks of relational knowledge. The capacity for such learning naturally depends on the architecture of the knowledge network itself. I will describe recent work assessing network constraints on the learnability of relational knowledge, and theories from statistical physics that offer an explanatory model for such constraints. I will then broaden the discussion to the generic manner in which humans communicate using systems of interconnected stimuli or concepts, from language and music, to literature and science. I will describe an analytical framework to study the information generated by a system as perceived by a biased human observer, and provide experimental evidence that this perceived information depends critically on a system's network topology. Applying the framework to several real networks, we find that they communicate a large amount of information (having high entropy) and do so efficiently (maintaining low divergence from human expectations). Moreover, we also find that such efficient communication arises in networks that are simultaneously heterogeneous, with high-degree hubs, and clustered, with tightly-connected modules -- the two defining features of hierarchical organization. Together, these results suggest that many real networks are constrained by the pressures of information transmission to biased human observers, and that these pressures select for specific structural features.
October 9 — "Discovering Neutrino Properties with Long-Baseline Beams"
- Presenter: Alysia Marino, University of Colorado, Boulder
- Host: John Cumalat
- Abstract: Neutrinos are fundamental particles with no electric charge and as-yet-unmeasured masses, allowing them to travel unimpeded through enormous amounts of material. Despite their elusiveness, a lot of compelling evidence shows that neutrinos have non-zero masses and change from one flavor to another. Intense neutrino beams generated by particle accelerators are now being used in order to more precisely probe the physics 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 16 — "Controlling magnetism in a Mott insulator by optical pumping"
- Presenter: David Hsieh, California Institute of Technology
- Host: Rahul Nandkishore
- Abstract: Controlling magnetism in an antiferromagnetic Mott insulator with ultrashort optical pulses can lead to both advances in our fundamental understanding of out-of-equilibrium interacting quantum matter as well as to novel high-speed information storage and processing technologies. However, optically manipulating antiferromagnetic order and detecting its out-of-equilibrium behaviors have proven difficult owing to various factors such as the absence of net magnetization and the ultrafast timescales involved. In this talk, I will describe a novel time-resolved nonlinear optical polarimetry technique that is capable of measuring ultrafast changes in magnetic symmetry. I will then describe how we have deployed this technique to reveal an unusual out-of-equilibrium critical behavior of the magnetic order in an optically pumped Mott insulator that circumvents the laws of equilibrium thermodynamics.
October 23 — "Frontiers of topological quantum matter and beyond"
- Presenter: Michael Hermele, University of Colorado, Boulder
- Host: John Cumalat
- Abstract: The last ten to fifteen years have witnessed extraordinary progress in the theory of topological quantum matter. This includes the discovery of new families of quantum phases of matter, going hand-in-hand with unprecedented advances in the systematic understanding of what phases are possible in principle. Progress has been particularly pronounced within a certain context that includes many physically interesting systems, but also leaves a vast frontier to explore. In this talk, I will describe two recent lines of work, one of which lies at this frontier, while the second crosses into ``non-topological’’ territory.
First, I will discuss crystalline topological phases, those where the geometrical symmetries of crystalline solids play an important role. Before the last few years, little was understood about such phases for strongly interacting systems, and obtaining such understanding was believed to be a hard problem. Surprisingly, due to previously hidden structure that my work uncovered, obtaining a systematic classification of crystalline topological phases turns out to be easier than for their non-crystalline counterparts.
Second, I will discuss so-called fracton phases of matter. While fracton phases share some features in common with topological phases, they are not topological. I will describe my work drawing connections between fracton phases and more familiar topological phases, and my ongoing contributions to the development of a theoretical framework for fracton matter.
October 30 — "Bringing Down the Cost of Fusion Power"
- Presenter: Steven Cowley, Princeton Plasma Physics Laboratory
- Host: Dmitri Uzdensky
- Abstract: The scientific demonstration of a self-sustained fusion burn in the international experiment ITER — is within sight. However, commercial fusion power will require further innovation to bring down the cost and complexity of fusion systems. I will describe recent advances in the science, design and technology of three-dimensional confinement devices (stellarators) that promise simpler and cheaper fusion reactors.
November 6 — "Making microwaves with light at the quantum limit and beyond"
- Presenter: Thomas Schibli, University of Colorado, Boulder
- Host: John Cumalat
- Abstract: Precision measurements enabled by exquisitely stable optical sources had a profound impact on Boulder’s current scientific enterprise. This talk will start with an overview of fundamental noise processes in oscillators, and highlight some of the major differences between electronic and optical sources. I will then discuss what levels of stability can be reached directly from a laser to date, and how to occasionally dip far below the quantum limit for specific applications.
As a practical application, I will elaborate on the generation of laser-driven, ultra-low noise microwaves, now readily surpassing the best room-temperature microwave sources at a fraction of their size, weight and power.
November 13 — "Quantum metrology at the 19th decimal place"
- Presenter: David Leibrandt, NIST, University of Colorado Boulder
- Host: John Cumalat
- Abstract: The tools of trapped-ion quantum logic can be used to enable and enhance precision measurements, with applications in time and frequency metrology and the search for physics beyond the standard model. In this talk, I will describe optical atomic clocks based on Al+ which operate at this fertile intersection of fields. These clocks use quantum-logic gates with a co-trapped second ion species for preparation and readout of the Al+ state, and offer the tantalizing prospect of Heisenberg-limited measurements with entangled ions. Recent progress, including an improved ion trap design and sympathetic laser cooling to the 3D ground state, has enabled total fractional systematic uncertainty below 10-18. We have performed frequency ratio measurements between Al+, Sr, and Yb clocks with uncertainty below 10-17, which can be used to place constraints on possible temporal variations of fundamental constants and models of ultralight dark matter.
November 20 — "Does an isolated quantum system relax?"
Presenter: Joerg Schmiedmayer, Vienna Center for Quantum Science and Technology (VCQ) Atominstitut – Institute of Atomic and Subatomic Physics Technische Universität- Host: Ana Maria Rey
- Abstract: The evolution of an isolated quantum system is unitary. This is simple to probe for small systems consisting of few particles. But what happens if the system becomes large and its constituents interact?
In a first set of experiments, we study a weak quench introducing quantum noise. The coherence created by coherent splitting of a 1d quantum gas degrades by coupling to the many internal degrees of freedom available [1]. The system relaxes to a pre-thermalisatized quasi steady state [2] described by a generalized Gibbs ensemble [3] which emerges through a light cone like spreading of ’de-coherence’ [4]. By engineering the Quasiparticles we can get coherence back by many body quantum revivals [5]. We conjecture that our experiments point to a universal way through which relaxation in isolated many body quantum systems proceeds if the low energy dynamics is dominated by scrambling of the eigenmodes of long lived excitations [6].
In a second set of experiments we study a strong cooling quench and demonstrate universal scaling in time and space, associated with the approach of a non-thermal fixed point [7]. The time evolution within the scaling period is described by a single universal function and scaling exponent, independent of the species of the initial state which constitutes a crucial step in the verification of universality far from equilibrium. If successful, this will lead to a comprehensive classification of systems far from equilibrium based on their universal properties similar to the universality classes in phase transitions. and be the basis for a new type of quantum simulation that let us explore a large variety of systems at different scales.
Work performed in collaboration with the groups of E. Demler (Harvard), Th. Gasenzer und J. Berges (Heidelberg). Supported by the Wittgenstein Prize, the FWF SFB FoQuS, DFG-FWF: SFB ISOQUANT: and the EU: ERC-AdG QuantumRelax
[1] S. Hofferberth et al. Nature, 449, 324 (2007).
[2] M. Gring et al., Science, 337, 1318 (2012); D. Adu Smith et al. NJP, 15, 075011 (2013).
[3] T. Langen et al., Science 348 207-211 (2015).
[4] T. Langen et al., Nature Physics, 9, 640–643 (2013).
[5] B. Rauer et al. Science 360, 307–310 (2018).
[6] T. Langen, T. Gasenzer, J. Schmiedmayer, J. Stat. Mech. 064009 (2016)
[7] S. Erne et al. Nature 253, 225 (2018).
November 27 — Fall Break, No Colloquium
December 4 — "Evaluating the Iran Nuclear Deal"
- Presenter: Ron Soltz, Lawrence Livermore National Laboratory
- Host: Jamie Nagle
- Abstract: The Iran Nuclear Deal evokes strong reactions. It has been called "The Worst Deal Ever" as well as "The best option for preventing Iran from obtaining a nuclear weapon. Otherwise known as the "Joint Comprehensive Plan of Action", the JCPOA has led to much debate, even if little of it has been substantive. Put into effect in 2015, the JCPOA continues to influence the behavior of the EU, China, and Russia, while the U.S. formally withdrew in May 2018 and Iran has recently begun to violate the agreement in stages.
The JCOPOA is unique in the history of international agreements, but as it stands at the intersection of science and policy, it is also a valuable teaching tool for the role that science can play in formulating good policy, while also providing an opportunity to review a few basic concepts in nuclear physics. I will review the basic components of the JCPOA and explain their origin. The agreement will also be placed in the context of past nuclear arms agreements and U.S. nuclear non-proliferation policy. I will review criticisms and flaws of the agreement. Future implications for Iran and global non-proliferation efforts will also be discussed.
December 11 — "The Challenge of a nuclear optical clock: recent progress and perspectives"
- Presenter: Lars von der Wense, Ludwig-Maximilians-University of Munich
- Host: Jun Ye
- Abstract: A nuclear optical clock based on a single 229Th ion is expected to achieve a higher accuracy than the best atomic clocks operational today [1]. Although already proposed back in 2003 [2], such a nuclear frequency standard has not yet become reality. The main obstacle that has so far hindered the development of a nuclear clock is an imprecise knowledge of the energy value of a nuclear excited state of the 229Th nucleus, generally known as the 229Th isomer. This metastable nuclear excited state is the one of lowest energy in the whole nuclear landscape and - with an energy of less than 10 eV - offers the potential for nuclear laser spectroscopy, which poses a central requirement for the development of a nuclear clock. In the past few years significant progress toward the development of a nuclear frequency standard has been made: Starting with a first direct detection of the 229Th isomer in 2016 based on its internal conversion decay channel [3], the isomeric lifetime could be determined in 2017 [4], followed by a first laser-spectroscopic characterization in 2018 [5]. Most recently, a first energy determination based on the isomer’s direct detection was successful [6]. This new knowledge provides, in combination with an achieved drastically enhancement of XUV-frequency comb intensity [7], the basis for improved efforts toward the laser-based search for the nuclear transition [8, 9], which can ultimately lead to the development of a nuclear optical clock. In this presentation I will give an overview over the current status of the nuclear clock development, with a particular focus on the most recent progress. Also the next required steps will be detailed and future perspectives will be given.
- References
[1] C.J. Campbell et al., Phys. Rev. Lett. 108, 120802 (2012).
[2] E. Peik and C. Tamm, Eur. Phys. Lett. 61, 181 (2003).
[3] L. von der Wense et al., Nature 533, 47 (2016).
[4] B. Seiferle et al., Phys. Rev. Lett. 118, 042501 (2017).
[5] J. Thielking et al., Nature 556, 321 (2018).
[6] B. Seiferle et al., Nature 573, 243 (2019).
[7] G. Porat et al., Nature Photonics 12, 387 (2018).
[8] L. von der Wense, Phys. Rev. Lett. 119, 132503 (2017).
[9] L. von der Wense and C. Zhang, arXiv:1905.08060 (2019).
For more information about colloquia this semester, contact: Rahul Nandkishore.
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 17 — "Can Evolutionary Dynamics Be Understood Quantitatively?"
- Presenter: Daniel Fisher, Stanford University
- Host: Leo Radzihovsky
- Abstract: The basic laws of evolution have been known for more than a century and there is overwhelming evidence for the facts of evolution. Yet little is understood quantitatively about the dynamical processes that drive evolution: by physicists' standards the theory of evolution is far from fully-fledged. Huge advances in DNA sequencing technology and laboratory experiments have enabled direct observations of evolution in action and, together with theoretical developments, opened up great opportunities for dramatically advancing our understanding. This talk will focus on framing questions and on recent progress addressing some of these.
January 24 — "Zen and the Art of Atomic Physics"
- Presenter: Eric Hudson, University of California, Los Angeles
- Host: John Bohn
- Abstract: In the Ten Bulls tradition, the fifth stage of Zen is reached when the practitioner has caught and tamed the wild bull. This is roughly the state of atomic physics. The atom has been tamed. It can be prepared in a single quantum state, its evolution coherently controlled, and its entanglement generated at will. As such, many new quantum-assisted technologies and fundamental physics measurements have resulted and a quantum revolution is well underway that promises to touch almost every aspect of our lives. By the seventh stage of Zen, the Bull has transcended and is no more. This again may be paralleled in atomic physics as the atom is being replaced with richer quantum systems such as molecules, whose internal degrees of freedom provide new opportunities for quantum science and technology.
In this talk, I will briefly review the science and technology that have come from atom taming and then discuss our efforts to tame other bulls: polar molecular ions and atomic nuclei.
January 31 — "Exploring the Ocean Worlds of the Outer Solar System for Life"
- Presenter: Jonathan Lunine, Cornell University
- Host: Sascha Kempf
- Abstract: Planetary exploration of the Jovian and Saturnian systems has revealed that three moons—Europa, Titan and Enceladus-- have either liquid water oceans or, for Titan, seas of hydrocarbons that are potentially interesting abodes for life. I will describe what we know of these bodies, in what way we think they are habitable, and a strategy to determine if life is present on any or all of them.
January 31 — "Exploring the Ocean Worlds of the Outer Solar System for Life"
- Presenter: Jonathan Lunine, Cornell University
- Host: Sascha Kempf
- Abstract: Planetary exploration of the Jovian and Saturnian systems has revealed that three moons—Europa, Titan and Enceladus-- have either liquid water oceans or, for Titan, seas of hydrocarbons that are potentially interesting abodes for life. I will describe what we know of these bodies, in what way we think they are habitable, and a strategy to determine if life is present on any or all of them.
February 7 — "Dirac, Jordan, and von Neumann: Hilbert space and transformation theory"
- Presenter: Michel Janssen, University of Minnesota
- Host: Allan Franklin
- Abstract: In early 1927, Paul Dirac and Pascual Jordan, independently of one another, published their versions of a general formalism tying the various forms of the new quantum theory together and giving the theory's statistical interpretation in full generality. This formalism has come to be known as the Dirac-Jordan (statistical) transformation theory. A few months later, in response to these publications by Dirac and Jordan, John von Neumann published his Hilbert space formalism for quantum mechanics. The relation between the two formalisms can be captured in terms of a metaphor of arches and scaffolds that I have argued fits a number of instances of theory change in physics. What is unclear in this case is whether the story is best told with Hilbert space playing the role of the arch built on transformation theory as a scaffold to be dismantled once the arch could support itself, or with transformation theory playing the role of the arch and Hilbert space providing the scaffold built to prevent the arch from collapsing under the weight of its serious mathematical deficiencies. Either way, a narrative for this episode in the history of quantum mechanics based on the arches-and-scaffolds metaphor illustrates the promise of borrowing ideas from the approach to evolutionary biology known as evodevo for reconstructing genealogies of theories rather than species.
**Special Physics Faculty Candidate Search Colloquium** Thursday, February 8 — "Exploring the hydrodynamic limit of many-body quantum systems"
- Presenter: Andrew Lucas, Harvard University
- Location and time: JILA X317, 4:00 p.m
- Host: Paul Romatschke
- Abstract: The emergence of hydrodynamics in complicated microscopic many-body models has been a problem of interest in physics for more than a century. I will describe two ways that the classical theory of hydrodynamics is still teaching us interesting things about interacting many-body quantum systems. Firstly, I will derive the constraints relating classical hydrodynamic phenomena to the spreading of quantum information. These bounds sharpen and clarify many previous conjectures on whether quantum fluids have the smallest diffusion constants allowed in nature. I will briefly outline how an exotic class of quantum systems, which are holographically dual to a black hole in one higher dimension, serve as highly non-trivial checks on these diffusion bounds. Secondly, I will describe hydrodynamic theories of transport in metals. Even though measuring the thermal and electrical conductivity of a metal is very easy experimentally, conventional approaches to transport theory are not adequate for metals where the electronic interactions are strong. I will describe recent experimental evidence for hydrodynamic transport, including dramatic violations of the Wiedemann-Franz law, and present a new mechanism for electron-limited transport, possibly applicable to single-band materials including SrTiO3.
**Special Physics Faculty Candidate Search Colloquium** Monday, February 12 — "How low can the energy density go?"
- Presenter: Aaron Wall, University of Maryland
- Location: DUAN G125
- Host: Paul Romatschke
- Abstract: Quantum fields can sometimes have negative energy density. In gravitational contexts, this threatens to permit both causality violations (such as traversable wormholes, warp drives, and time machines) and violations of the Second Law for black holes. I will discuss the thermodynamic principles that rule out such pathological situations. These principles have led us to an interesting lower bound on the energy flux, even for field theories in flat spacetime!
This Quantum Null Energy Condition has recently been proven for general relativistic field theories. I will give an intuitive argument explaining why such ``quantum energy conditions'' ought to hold.
February 14 — "Who ordered that: what lepton flavor may tell us about the Universe"
- Presenter: Yury G. Kolomensky, University of California, Berkeley
- Host: Eric Zimmerman
- Abstract: Muons, heavy cousins of electrons whose existence famously puzzled I.I. Rabi, may play an important role in understanding the behavior of particles and fields at the highest energies. Searches for transitions that violate the apparent lepton flavor conservation are sensitive to new interactions with the energy scale above those accessible in the modern colliders. Recent hints of deviations from the Standard Model expectations in the processes involving muons are intriguing, and motivate new measurements over the next decade. Among those, the Mu2e experiment at Fermilab will search for neutrinoless muon-to-electron conversion with unprecedented precision. I will discuss the history of the lepton flavor measurements, and describe the design and present status of Mu2e, which will improve the current constraints by four orders of magnitude.
**Special Physics Faculty Candidate Search Colloquium** Thursday, February 15 — "Sources of student interest and engagement in Introductory Physics for Life Science"
- Presenter: Ben Geller
- Location: JILA Auditorium
- Time: 3:00 - 4:00 p.m.
- Host: Heather Lewandowski
- Abstract: Effectively teaching an Introductory Physics for Life Science (IPLS) course means engaging life science students in a subject for which they may not have considerable preexisting interest. We have found that the inclusion of topical examples of relevance to life-science students can help to engage students whose initial interest in physics is less developed, but that different examples and models vary in their effectiveness. Examples that ground physical models in authentic biological and biochemical contexts with which the students are already familiar, and about which they may already have authentic driving questions, are especially effective. By analyzing data from (1) survey instruments assessing student attitudes and interest in particular life science examples, and (2) interviews conducted with students before and after instruction, we identify features of our IPLS course that appear to be particularly important for fostering student learning and engagement. We suggest that some of these features might also foster student interest in more traditional introductory physics courses.
**Special Physics Faculty Candidate Search Colloquium** Thursday, February 15 — "Holographic phase diagrams"
- Presenter: Christiana Pantelidou, Imperial
- Location: JILA X317
- Host: Paul Romatschke
- Abstract: Over the last 20 years, the Gauge/Gravity correspondence has led to significant progress in the understanding of strongly coupled matter without quasiparticles, found both in Condensed Matter systems and Quantum Chromodynamics. In this talk, after an extended pedagogical introduction on the subject, I will discuss the various phases that have been discovered using this approach, how they compete with each other and what is currently known about their ground states.
**Special Physics Faculty Candidate Search Colloquium** Monday, February 19 — "The atoms of an expanding universe"
- Presenter: Dionysios Anninos, Harvard University
- Location: DUAN G125
- Host: Paul Romatschke
- Abstract: Observations over the past few decades have provided important evidence about the geometry of the large-scale universe.
During the early inflationary era, as well as the current vacuum dominated era, the evidence points to a universe described by an exponentially expanding de Sitter spacetime. From the perspective of theoretical physics, the last two decades have seen remarkable progress in our understanding of spacetime as an emergent, collective phenomenon stemming from a microscopic holographic system with a large number of `atomic' constituents. This has been achieved with great success for negatively curved anti-de Sitter spacetimes. We will explore holography for a de Sitter universe. Our discussion will be guided by the construction and consideration of concrete mathematical models, providing an exact realization of the dS-CFT correspondence.
We will also discuss similarities and distinctions between the cosmological horizon of a de Sitter universe and the horizon of an ordinary black hole from a modern, holographic perspective.
February 21 — "Superconducting Microresonators: From Astrophysics to Zero-Point Fluctuations"
- Presenter: Jonas Zmuidzinas, Caltech
- Host: Jason Glenn
- Abstract: The hallmark of superconductivity – zero electrical resistance – explains why superconducting resonators can have very low dissipation (high Q). Superconducting resonators at the macro scale have been developed for decades and enable energy-efficient high-energy accelerators such as the LHC. At the micro scale, superconducting resonators have attracted considerable attention in recent years and are being applied to a rapidly growing range of applications, from photon detectors for astrophysics to quantum circuits. This presentation will describe the advances in superconducting microresonators over the past two decades, focusing on their use as detectors and the relevant physical phenomena, but including a wide variety of other applications.
February 28 — "Command of Swimming Bacteria by Liquid Crystals"
- Presenter: Oleg Lavrentovich, Kent State University
- Host: Joe MacLennan
- Abstract: Self-propelled bacteria are marvels of nature. If we can control their dynamics, we could use it to power microsystems of the future. Unfortunately, bacteria swim mostly randomly in isotropic liquids such as water. It is difficult to control their dynamics by factors other than transient gradients of nutrients; visual, acoustic and tactile communication channels that humans use to control large animals are not effective. To establish communication, we replace water with a water-based lyotropic liquid crystal, which couples propulsion of bacteria to the orientational order of the medium. The long-range orientational order of the liquid crystal can be designed as uniform or be pre-patterned into various structures by a plasmonic photoalignment technique [1]. The preimposed patterns of liquid crystal orientation allow one to gain a significant control over the dynamics of bacteria, namely, their trajectories, polarity of swimming, spatial variation of concentration [2], and run-and-tumble behavior [3]. Topological defects of integer strength serve either as attractors or repellents of bacteria, while defect pairs and patterns with broken left-right symmetry pump the bacterial flows along a preselected polar axis. The study of bacteria-liquid crystal system might result in approaches to harness the energy of collective motion for micro-robotic, biomechanical, and sensing devices, as well as micro-mixing and transport of micro-cargo. The work is supported by NSF grants DMR-1507637 and DMS-1729509.
March 7 — "EPR and spatial-mode entanglement in spinor Bose-Einstein condensates"
- Presenter: Carsten Kempt, Institut für Quantenoptik, Leibniz Universität Hannover
- Host: Ana Maria Rey
- Abstract: Spin changing collisions in alkaline Bose-Einstein condensates can be employed to generate highly entangled atomic quantum states. Here, we will report on the generation of two classes of entangled states. Firstly, we demonstrate the generation of two-mode squeezed vacuum states and record their characteristic quadrature correlations by atomic homodyning. We prove that the correlations fulfill Reid’s criterion [1] for continuous-variable Einstein-Podolsky-Rosen entanglement. The homodyne measurements allow for a full tomographic reconstruction, yielding a two-mode squeezed state with a 78% fidelity. The created state can be directly applied to atom interferometry, as is exemplified by an atomic clock measurement beyond the Standard Quantum Limit.
Secondly, we demonstrate entanglement between two spatially separated atomic modes. The entangled state is obtained by spatially splitting a Twin Fock state of indistinguishable atoms. The method opens a path to exploit the recent success in the creation of many-particle entanglement in ultracold atoms for the field of quantum information, where individually addressable subsystems are required. Finally, we will show how the measurement protocol can be extended to perform a Bell test of quantum nonlocality.[1] M. Reid, Phys. Rev. A 40, 913–923 (1989)
March 14 — "Throwing God's Dice"
- Presenter: Krister Shalm, NIST
- Host: John Price
- Abstract: In 1943 Einstein wrote to Max Born saying “As I have said so many times, God doesn't play dice with the world.” This discussion with Born was just one part of a much large debate on the consequences of quantum theory on the nature of reality. In 1935 Einstein, Podolsky, and Rosen famously published a paper with the aim of showing that the wave function in quantum mechanics does not provide a complete description of reality. The gedanken experiment showed that quantum theory, as interpreted by Niels Bohr, leads to situations where distant particles, each with their own “elements of reality”, could instantaneously affect one another. Such action at a distance seemingly conflicts with relativity. The hope was that a local theory of quantum mechanics could be developed where individual particles are governed by elements of reality, even if these elements are hidden from us. In such a theory, now known as local realism, these elements of reality or hidden variables could remove the randomness inherent in quantum mechanics.
In 1964 John Bell in a startling result showed that the predictions of quantum mechanics are fundamentally incompatible with any local realistic theory. In other words, an experiment can be done that can rule out all theories based on local hidden variables. Carrying out this test has been technologically challenging. It wasn’t until 2015 when three independent groups were able to rule out local realism in experiments free of loopholes. In this talk I will discuss the loophole-free Bell test carried out at the National Institute of Standards and Technology. I will also discuss how we can use such a Bell test to build a random number generator that can be certified by quantum mechanics itself. Such a random number generator that can trace its roots back to the original Einstein thought experiments is the closest we can get to “throwing God’s dice.”
March 21 — "Exploring the 3D Nano and Atomic World: Coherent Diffractive Imaging and Atomic Electron Tomography"
- Presenter: John Miao, Deputy Director, NSF STROBE Science and Technology Center, Department of Physics and Astronomy and California NanoSystems Institute, University of California Los Angeles
- Host: Margaret Murnane
- Abstract: The discovery and analysis of X-ray diffraction from crystals by Max von Laue, William Henry Bragg and William Lawrence Bragg in 1912 marked the birth of crystallography. Over the last century, crystallography has been fundamental to the development of many fields of science. However, many samples in physics, chemistry, materials science, nanoscience, geology, and biology are non-crystalline, and thus their 3D structures are not accessible by traditional crystallography. Overcoming this major hurdle has required the development of new structure determination methods. In this talk, I will present two methods that can go beyond crystallography: coherent diffractive imaging (CDI) and atomic electron tomography (AET). In CDI, the diffraction pattern of a non-crystalline sample or a nanocrystal is first measured and then directly phased to obtain an image. The well-known phase problem is solved by combining the oversampling method with iterative algorithms. In the first part of the talk, I will illustrate several prominent CDI methods and highlight some important applications using high harmonic generation, 3rd generation synchrotron radiation and X-ray free electron lasers. In the second part of the talk, I will present a general tomographic method, termed AET, for 3D structure determination of crystal defects and disordered materials at atomic resolution. By combining advanced electron microscopes with novel data analysis and powerful computational algorithms, AET has been used to reveal the 3D atomic structure of crystal defects and chemical order/disorder, and to precisely localize the 3D coordinates of individual atoms in materials without assumption of crystallinity. The experimentally measured coordinates can then be used as direct input for quantum mechanical calculations of physical properties such as atomic spin and orbital magnetic moments and local magnetocrystalline anisotropy at the single-atom level. As large-scale and tabletop coherent X-ray sources and powerful electron microscopes are under rapid development worldwide, CDI and AET are expected to find broad applications in both the physical and biological sciences.
1. J. Miao, T. Ishikawa, I. K. Robinson and M. M. Murnane, “Beyond crystallography: Diffractive imaging using coherent x-ray light sources”, Science 348, 530-535 (2015). (Review)
2. J. Miao, P. Ercius and S. J. L. Billinge, "Atomic electron tomography: 3D structures without crystals", Science 353, aaf2157 (2016). (Review)
3. Y. Yang, C.-C. Chen, M. C. Scott, C. Ophus, R. Xu, A. Pryor Jr, L. Wu, F. Sun, W. Theis, J. Zhou, M. Eisenbach, P. R. C. Kent, R. F. Sabirianov, H. Zeng, P. Ercius and J. Miao, “Deciphering chemical order/disorder and material properties at the single-atom level”, Nature 542, 75-79 (2017).
March 28 — Spring Break; No Colloquium
April 4 — "Quantum-limited measurements: One physicist's crooked path from quantum optics to quantum information"
- Presenter: Carlton Caves, University of New Mexico
- Host: Scott Diddams
- Abstract: Quantum information science has changed our view of quantum mechanics. Originally viewed as a nag, whose uncertainty principles restrict what we can do, quantum mechanics is now seen as a liberator, allowing us to do things, such as secure key distribution and efficient computations, that could not be done in the realistic world of classical physics. Yet there is one area, that of quantum limits on high-precision measurements, where the two faces of quantum mechanics remain locked in battle. I will trace the history of quantum-limited measurements, from the use of nonclassical light to improve the phase sensitivity of an interferometer, to the modern perspective on the role of entanglement in improving measurement precision.
April 11 — "From the Einstein-Bohr debate to quantum information: the second quantum revolution"
- Presenter: Alain Aspect, Institut d’Optique Graduate School, Palaiseau
- Host: Jun Ye
- Abstract: In 1935, with co-authors Podolsky and Rosen, Einstein discovered a weird quantum situation, in which particles in a pair are so strongly correlated that Schrödinger called them “entangled”. By analyzing that situation, Einstein concluded that the quantum formalism is incomplete. Niels Bohr immediately opposed that conclusion, and the debate lasted until the death of these two giants of physics.
In 1964, John Bell discovered that it is possible to settle the debate experimentally, by testing the now celebrated "Bell's inequalities", and to show directly that the revolutionary concept of entanglement is indeed a reality. A long series of experiments, started in 1972, have produced more and more precise results, in situations closer and closer to the ideal theoretical scheme.
After explaining the debate, and describing some experiments, I will show how this conceptual discussion has prompted the emergence of the new field of quantum information, at the heart of the second quantum revolution.
**Special Physics Faculty Candidate Search Colloquium** Tuesday, April 17 — "Polarization in spectral lines: a window into the physics of the solar atmosphere"
- Presenter: Ivan Milić, Max Planck Institute for Solar System Research
- Location and time: JILA Auditorium, 4:00 p.m
- Host: Dmitri Uzdensky
- Abstract: The light that we receive from the Sun has passed through the solar atmosphere and undergone many scattering processes that leave their imprint on its spectral distribution and polarization state. These processes are influenced by the thermodynamic and magnetic properties of the plasma and thus the spectropolarimetric observations in spectral lines allow us to infer the temperature, velocity and magnetic field throughout the solar atmosphere.
This talk will focus on the Zeeman effect, scattering polarization and the Hanle effect, and how they contribute to form line polarization patterns. More specifically, the emphasis will be on spectral lines formed in non-local thermodynamic equilibrium conditions. Such lines typically probe the physical conditions in the upper layers of solar atmosphere, regions that are particularly interesting for their highly dynamic and magnetic nature. The diagnostic techniques, however, can be extended to a multitude of astrophysical objects, such as atmospheres of other stars and different types of accretion or circumstellar disks.
We will also discuss spectropolarimetric inversions, as the state-of-the-art tools used for the interpretation of the solar observations with high angular and spectral resolution. Finally, a brief outlook on the bright future of the field, especially in the light of Daniel K. Inouye Solar Telescope, will be presented.
Image: Observed intensity and circular polarization (top two panels), and inferred temperature, line-of-sight velocity and line-of-sight magnetic field at two different depths in an observed patch of the solar atmosphere.
April 18 — "Optical atomic clock: a case study for the quantum technology revolution"
- Presenter: Jun Ye, JILA, University of Colorado Boulder
- Host: John Price
- Abstract: Precise quantum state engineering of individual atoms has led to the unprecedented measurement performance for time and frequency. The use of many atoms not only enhances the counting statistics, but is also emerging as a powerful tool to protect against systematic uncertainties. At the core of the new JILA three-dimensional optical lattice clock is a quantum gas of fermionic atoms that are spatially correlated to guard against motional and collisional effects. The convolution of precision control of light and matter is helping bridge different disciplines in physics and fostering new capabilities to probe fundamental and emerging phenomena.
**Special Colloquium** Wednesday, April 25 — "Driven Phases of Many-Body Quantum Matter"
- Presenter: Vedika Khemani, Harvard University
- Location and time: JILA Auditorium, 12:00 p.m
- Host: Leo Radzihovsky
- Abstract: Recent years have witnessed a remarkable confluence of diverse areas of physics coming together to inform fundamental questions about many-body quantum matter. A unifying theme in this enterprise has been the study of many-body quantum dynamics in systems ranging from electrons in solids to cold atomic gases to black holes. One of the foundational pillars in the study of many-body systems is the theory of equilibrium statistical mechanics characterized by two fundamental ideas: thermalization (that interacting systems generically approach thermal equilibrium at late times) and phase structure (that equilibrium states of matter can display various forms of order separated by sharp phase transitions).
Recent progress, particularly in the field of many-body localization, has led to generalizations of these fundamental ideas to the out-of-equilibrium setting. I will describe this progress, particularly as applied to periodically driven or Floquet systems. I will show that not only can non-equilibrium systems exhibit a sharp notion of phase structure, but that some of these phases are completely novel and unique to the out-of-equilibrium setting. For example, certain phases of matter that are forbidden in equilibrium, such as quantum time crystals, have found new life in the out-of-equilibrium setting. I will describe some of the many fascinating properties of this phase, and comment on recent experiments that have detected signatures of time crystals in a variety of different physical settings.
April 25 — "Hot tips for thermal nanophysics"
- Presenter: Fabian Menges, University of Colorado, Boulder
- Host: John Price
- Abstract: Temperature is one of the most central concepts of thermal physics with historical roots in the seventeenth century mechanics and nineteenth century thermodynamics. Building up on these early foundations, I will highlight how the understanding of temperature gets increasingly challenging when small systems are away from equilibrium, get scaled to ensemble sizes below classical limits, and when quantum effects become relevant. Today, the apparently simply question of ‘what is the temperature’ is again up for debate, fueled by the miniaturization of technology and the experimental progress to study physical properties and processes down to atomic length and ultrafast time scales. Aiming to clarify questions such as how to measure temperature on the length-scale of nanoscale transistors, how interfaces and contacts influence dissipation processes, and how fundamental heat and charge transport relations may change at the atomic scale, we have recently developed new thermal nanometrology techniques based on scanning probe methods [1]. By demonstrating the real-space quantification of local Joule and Peltier effects at metal-semiconductor contacts [2], and the first atomic scale validation of the Wiedemann-Franz law at room temperature [3], I will illustrate the application of these approaches. Finally, I’ll provide an outlook on our ongoing efforts to open the door for spatio-temporal characterization of thermal phenomena at the transition from the classical to the quantum regime.
References:
[1] F. Menges et al., Nanoscale thermometry by scanning thermal microscopy, Review of Scientific Instruments (87) 7, 074902, 2016.
[2] F. Menges et al., Temperature mapping of operating nanoscale devices by scanning probe thermometry, Nature Communications 7(10874), 2016.
[3] N. Mosso et al., Heat transport through atomic contacts, Nature Nanotechnology 12, 430-433, 2017.
May 2 — "The Quest for a Quantum Spin Liquid*"
- Presenter: Collin Broholm, Johns Hopkins University
- Host: Dmitry Reznik
- Abstract: Magnetism has commanded human wonder through millennia and it is a central component of the technologies that shape our lives. For the past 50 years scientists have been in pursuit of a radically new form of magnetism that would constitute a new state of matter: The quantum spin liquid may exist within a crystalline solid composed of atoms that carry a magnetic dipole moment. However, quantum fluctuations of these dipole moments preclude the development of conventional magnetic order even at temperature far below the scale of inter-site interactions. The result is a quantum material with unique macroscopic properties driven by quantum coherence and entanglement. If we can realize the materials physics of the quantum spin liquid these properties can be fully explored and might lead to interesting applications much as other advances we have made in our understanding of magnetism.
In the ongoing quest for a robust realization of a quantum spin liquid in the lab, a range of interesting magnetic materials and phenomena have been discovered. I shall review experiments probing interacting quantum spins on kagome, honeycomb, and triangular lattices in 2D and on the pyrochlore lattice in 3D. These frustrated quantum magnets feature an intermediate energy and temperature regime with spin-liquid-like properties but also unique low temperature phases driven by quenched disorder or lattice instabilities. Such inevitable deviations from ideal spin liquid models are interesting in their own right and their elucidation may contribute to understanding age old puzzles such as the phase diagram of V2O3 which I shall describe in greater detail in my seminar the following day.
* Supported by U.S. DoE Basic Energy Sciences, DE-FG02-08ER46544 and by the Gordon and Betty Moore foundation GBMF 4532.
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"
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
- 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.
November 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"
NOTE 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.
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.
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.
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