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.

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 theses 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 

  • Presenter: Colin Broholm, Johns Hopkins University
  • Host: Dmitry Reznik
  • Abstract:

Previous Colloquia

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.

Graphic of observed intensity and circular polarization, as described in April 17 abstract**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.

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