Colloquia are Wednesdays at 4:00 p.m. in the JILA Auditorium. 

Coffee, tea and cookies will be available in G1B31 (across from G1B20) from 3:30 - 3:50 p.m.

To view recordings of each regular colloquium lecture, please go to the Spring 2023 Physics Colloquia YouTube Playlist.

To view recordings of each special colloquium lecture, please go to the Spring 2023 Special Colloquia YouTube Playlist.

**Canceled** January 18 — "The Fascinating History of Numbers in Ancient Mesopotamia"

  • Presenter: Jeanne Nijhowne, University of Colorado, Boulder
  • Host: Paul Beale
  • Abstract: For tens of thousands of years, humans got along perfectly well without numbers as we understand them. Then around 5000 years ago for reasons that remain unclear, people in the ancient Near East began living in cities with monumental architecture, civil and religious bureaucracies, centralized food distribution systems, and long-distance trading networks. It was simply not possible to run such complex societies without some kind of accounting system or knowledge of mathematical principles. This lecture concentrates on the long, and dare I say “tortured” history of Mesopotamian counting systems. The developments in numbers and mathematics will be discussed in their cultural context in an effort to explain why changes happened as they did and their legacy still influencing us today.
    Jeanne Nijhowne holds a Ph.D. in Anthropology with a specialty in the archaeology of the ancient Near East. She has worked on archaeological excavations in Egypt, Iraq, Turkey, Jordan and Syria ranging in time from the 8th millennium B.C. to the 4th century A.D. She currently works as the Graduate Program Assistant in the Department of Physics and teaches a summer class on Mesopotamian archaeology for the Anthropology Department at CU.

SPECIAL Physics Colloquium — Tuesday, January 24, 2:00 p.m.

  • Title: "From Quantum Information to the Black Hole Interior"
  • Presenter: Ying Zhao, Kavli Institute for Theoretical Physics, University of California Santa Barbara
  • Host: Oliver DeWolfe
  • Abstract: Black holes have not just become laboratories for astronomers, but also present some of the deepest unsolved problems in theoretical physics. During the past decade surprising connections have been made between ideas from quantum information and gravitational physics. In this talk I will explain several aspects of these connections. In particular, we will see that by treating a black hole as a quantum computer, we can understand various properties of the black hole interior. I will also show you how the black hole information puzzle can be understood from this point of view. 

January 25 — "The Absurd and Useful Physics of Atomtronics"

  • Presenter: Dana Anderson, University of Colorado, Boulder • JILA
  • Host: Leo Radzihovsky
  • Abstract: Atomtronics, an ultracold atom analog of electronics, provides a practical pathway for utilizing the quantum character of ultracold atoms in a variety of compelling applications involving sensing and signal processing. The atomtronic transistor, for example, is an analog of the electronic transistor that is exceedingly useful for creating amplifiers, oscillators, switches and so on. The understanding of atomtronic circuitry takes us to fundamental depths of field theory applied to a very practical domain. Along with many familiar parallels to Maxwell’s equations and electromagnetics, the physics of atomtronics is also surprising, sometimes seemingly absurd. I will take some time to draw the connection between fundamental physics starting with CU’s Nobel-recognized accomplishments in Bose-Einstein Condensation and the impact on and by the very practical technology developed by CU spinoff ColdQuanta (now Infleqtion), recently honored to have one of Time’s 2022 Invention of the year award for its quantum matter machine “Albert” that is used for developing atomtronic circuits.

SPECIAL Physics Colloquium — Thursday, January 26, 2:00 p.m.

  • Title: Quantum Simulation for High-Energy Physics
  • Presenter: Federica Maria Surace, California Institute of Technology
  • Host: Oliver DeWolfe
  • Abstract: Simulating strongly interacting quantum systems is a difficult task: as a prominent example, solving the fundamental equations of the quantum chromodynamics theory of quarks and gluons requires non-perturbative approaches based on computationally-expensive Monte Carlo simulations. The need for alternative solutions that do not rely on Monte Carlo methods has recently motivated an increasing interest in the possible applications of quantum simulation and computation. In this talk, I will review the recent advances in the field of quantum simulation for high-energy physics, with a special focus on analog simulators based on ultra-cold atoms. These controllable quantum systems can be used to simulate a variety of phenomena, including confinement, particle collisions, and false vacuum decay.

SPECIAL Physics Colloquium — Tuesday, January 31, 2:00 p.m.

  • Title: Quantum Computational Advantage: Recent Progress and Next Steps
  • Presenter: Xun Gao, Harvard University
  • Host: Oliver DeWolfe
  • Abstract: This talk is motivated by the question: why do we put so much effort and investment into quantum computing? A short answer is that we expect quantum advantages for practical problems. To achieve this goal, it is essential to reexamine existing experiments and propose new protocols for future quantum advantage experiments.
    In 2019, Google published a paper in Nature claiming to have achieved quantum computational advantage, also known as quantum supremacy. In this talk, I will explain how they arrived at their claim and its implications. I will also discuss recent theoretical and numerical developments that challenge this claim and reveal fundamental limitations in their approach.
    Due to these new developments, it is imperative to design the next generation of experiments. I will briefly mention three potential approaches: efficiently verifiable quantum advantage, hardware-efficient fault-tolerance, and quantum algorithms on analog devices for practical problems, including machine learning and combinatorial optimization.

February 1 — "Arrays of Individually-Controlled Molecules for Quantum Science"

  • Presenter: Kang-Kuen Ni, Department of Chemistry, Harvard University
  • Host: Jun Ye, Ana Maria Rey
  • Abstract: Advances in quantum manipulation of molecules bring unique opportunities: the use of molecules to search for new physics; exploring chemical reactions in the ultra-low temperature regime; and harnessing molecular resources for quantum simulation and computation. I will introduce our approaches to building individual ultracold molecules in optical tweezer arrays with full quantum state control. This work expands the usual paradigm of chemical reactions that proceed via stochastic encounters between reactants, to a single controlled reaction of exactly two atoms. The new technique allows us to isolate two molecular rotational states as two-level systems for qubits.  In order to preserve coherence of the qubits, we develop magic-ellipticity polarization trapping. Finally, we are taking advantage of the resonant dipolar interaction of molecules to entangle them with single site addressability. In combination, these ingredients will allow the molecular quantum system to be fully programmable. 

SPECIAL Physics Colloquium — Tuesday, February 7, 2:00 p.m.

  • Title: Error Correction in Quantum Computers and Beyond
  • Presenter: Aleksander Kubica, Amazon Web Services Center for Quantum Computing and California Institute of Technology
  • Host: Oliver DeWolfe
  • Abstract: Quantum computers introduce a radically new paradigm of information processing and revolutionize our thinking about the world. However, designing and building quantum computers that operate properly even when some of their components malfunction and cause errors is a heroic endeavor. In this talk, I will explain how quantum error correction and the theory of fault tolerance are indispensable to achieve this task. I will also discuss the profound impact of quantum error correction on our understanding of nature, ranging from new insights into quantum many-body physics to fundamental limitations on sensing and computation.

February 8 — "Waves Affect and Detect Climate"

  • Presenter: Baylor Fox-Kemper, Brown University
  • Host: Michael Ritzwoller
  • Abstract: Ocean surface gravity waves, the ones familiar to surfers and beachgoers, are mostly generated by winds.  Because they are the most direct way that winds affect the ocean, they both affect the climate system and are used in the detection of climate change.  It is difficult to measure the winds everywhere on earth, but detection of ocean waves from satellites provides a near-global view into their continual change.  Over long distances, changes in the waves accumulate the history of the winds that blow over them, so changes in the waves are both an impact (through coastal inundation) and detector of climate change.  Waves also link closely to ocean turbulence, ocean currents, and sea ice breakup.  Nobelist Irving Langmuir first described a key consequence of ocean turbulence driven by waves--windrows where flotsam such as pollution (oil and plastics), seafoam, and seaweed accumulates.  Accounting for this wave-driven turbulence in climate models has improved our ability to project future global warming, and future improvements in modeling waves' effects on sea ice and currents lay ahead.

SPECIAL Physics Colloquium — Thursday, February 9, 2:00 p.m.

  • Title: The Black Hole Information Paradox and Quantum Codes
  • Presenter: Christopher Akers, Massachusetts Institute of Technology
  • Host: Oliver DeWolfe
  • Abstract: In 1974, Stephen Hawking argued that black holes destroy information, counter to a fundamental principle in quantum mechanics, calling into question how general relativity and quantum mechanics could ever be unified. Ever since then physicists have wrestled with this question. I will explain the history of this debate, with a focus on modern developments that use ideas from the theory of quantum information and computation to finally offer a sharp resolution.

SPECIAL Physics Colloquium — Tuesday, February 14, 2:00 p.m.

  • Title: Tailoring Quantum Error Correction for Structured Noise
  • Presenter: Jahan Claes, Yale University
  • Host: Oliver DeWolfe
  • Abstract: Large-scale quantum computers will require error correction in order to reliably perform computations. However, the hardware overhead for error correction remains dauntingly large, with each logical qubit potentially requiring thousands of physical qubits for reliable operation. One promising approach to reducing the overheads of error correction is to tailor quantum error correcting codes to the dominant noise in the qubit hardware.
    In this talk, I’ll present recent work on tailoring measurement-based quantum computing to biased noise. In the first part of the talk, I’ll explain the basics of measurement-based error correction and cluster states, and show how a cluster state derived from the XZZX surface code, the so-called XZZX cluster state, can effectively correct biased noise. In the second part of my talk, I’ll present two applications of the XZZX cluster state for increasing thresholds in both linear optical qubits and Rydberg atoms. These works demonstrate that carefully considering the dominant hardware noise when designing error correction protocols can drastically increase their effectiveness.

February 15 — "Ab initio approaches to driven quantum matter and quantum information science"

  • Presenter: Prineha Narang, University of California, Los Angeles
  • Host: Leo Radzihovsky
  • Abstract: In this talk, I will present theoretical and computational approaches to describe excited-states in quantum matter, and predicting emergent states created by external drives. Understanding the role of such light-matter interactions in the regime of correlated electronic systems is of paramount importance to fields of study across condensed matter physics, quantum optics, and ultrafast dynamics. The simultaneous contribution of processes that occur on many time and length-scales have remained elusive for state-of-the-art calculations and model Hamiltonian approaches alike, necessitating the development of new methods in computational physics. I will discuss our work at the intersection of ab initio cavity quantum-electrodynamics and electronic structure methods to treat electrons, photons and phonons on the same quantized footing, accessing new observables in strong light-matter coupling. Current approximations in the field almost exclusively focus on electronic excitations, neglecting electron-photon effects, for example, thereby limiting the applicability of conventional methods in the study of polaritonic systems, which requires understanding the coupled dynamics of electronic spins, nuclei, phonons and photons. With our approach we can access correlated electron-photon and photon-phonon dynamics, essential to our latest work on driving quantum materials far out-of-equilibrium to control the coupled electronic and vibrational degrees-of-freedom. In the second part of my talk, I will demonstrate how the same approach can be generalized in the context of control of molecular quantum matter and quantum transduction with implications for scalable quantum architectures.
    Dr. Prineha Narang is a Professor in Physical Sciences at UCLA. Her group works on theoretical and computational quantum materials, non-equilibrium dynamics, and transport in quantum matter. Outside of science, she is an avid triathlete, runner, and starting her mountaineering journey.

SPECIAL Physics Colloquium — Thursday, February 16, 2:00 p.m.

  • Title: Long-range Entanglement and Topological States in Quantum Devices: from Hamilton to Galois
  • Presenter: Ruben Verresen, Harvard University
  • Host: Oliver DeWolfe
  • Abstract: One of the most remarkable discoveries in quantum physics is that long-range entangled qubits can give rise to emergent gauge fields and collective excitations exhibiting generalized ('anyonic') exchange statistics. Despite the importance of such 'topological' states for quantum information processing, they are extremely challenging to find in materials. In this talk, we explore how novel 'bottom-up' quantum devices---built atom by atom, qubit by qubit---challenge this status quo. For instance, topological states can emerge as the low-energy description of a many-body Hamiltonian, with experimental data on Rydberg atom tweezer arrays. Alternatively, such long-range entanglement can be obtained from shallow circuits with measurements and feedforward, with experimental data on cold ions. Only the latter route is able to avoid fundamental constraints imposed by locality and unitarity, leading to a surprising connection to the unsolvability of the quintic.

February 22 — "How Much Information Is In A Quantum State?"

  • Presenter: Scott Aaronson, Computer Science, University of Texas Austin
  • Host: Leo Radzihovsky
  • Abstract: To describe an entangled state of n particles, we formally need an amount of classical information that grows exponentially with n.  But given that almost all the information disappears on measurement, in what sense was it "really there"?  In this talk, I'll first survey a career's-worth results showing that, for many purposes, quantum states can effectively be described with vastly less classical information. In the other direction, however, I'll discuss the exponential separation between quantum and randomized communication complexities due to Bar-Yossef, Jayram, and Kerenidis, as well as brand-new work by me, Buhrman, and Kretschmer, which builds on their separation to show that "FBQP/qpoly != FBQP/poly" (unconditionally, there exist relational problems solvable using quantum advice but not classical advice).  I'll end by explaining how this theorem directly suggests a new type of quantum supremacy experiment -- one that, in contrast to the recent supremacy experiments by Google, USTC, and Xanadu, would not depend on any unproved computational hardness assumptions, but would seek a direct "experimental witness for the vastness of n-particle Hilbert space."  I believe this type of experiment is just now becoming technologically feasible.

March 1— "Stacking van der Waals atomic layers: quest for new quantum materials"

  • Presenter: Philip Kim, Harvard University
  • Host: Leo Radzihovsky
  • Abstract: Modern electronics rely heavily on technology that confines electrons in the interface layers of semiconductors. In recent years, scientists have discovered that they can isolate various atomically thin van der Waals (vdW) layered materials. In these atomically thin materials, quantum physics allows electrons to move only in an effective 2-dimensional (2D) space. By stacking these 2D quantum materials, one can also create atomically thin vdW heterostructures with a wide variety of electronic and optical properties. In this talk, we will discuss several research efforts to realize emergent physical phenomena in stacked vdW interfaces between 2D materials.

March 8 — "Lise Meitner, Her Escape from Germany and the Discovery of Fission"

  • Presenter: Anthea Coster, Massachusetts Institute of Technology
  • Hosts: Allan Franklin and Leo Radzihovsky
  • Abstract: Lise Meitner was one of the pioneers of nuclear physics and co-discoverer, with Otto Hahn and Fritz Strassmann, of nuclear fission. Albert Einstein once called her, "the most significant woman scientist of the 20th century". Yet by the 1970's, her name was nearly forgotten. With the publication of the book by Ruth Lewin Sime, "Lise Meitner, A life in physics," to some extent her name has resurfaced. The chronology of the discovery of fission is considerably more complex than the facts, and clouded by events beyond the world of science. The facts are that on January 6, 1939, Hahn and Strassmann reported in Naturwissenschaften their chemical findings for fission. On February 11, 1939, Meitner and Frisch published in Nature the physical interpretation of the process they named fission. In 1944, Otto Hahn alone received the Nobel Prize in Chemistry "for his discovery of the fission of heavy nuclei."

    I became familiar with Lise Meitner and her story when, in 1972, Dr. Sime started writing my father for details about Lise Meitner's escape from Germany. This is because in July 1938, my grandfather, Dirk Coster, was the person who escorted her out of Germany. In Sime's book, Meitner’s escape from Germany reads like a spy novel, except that it is completely based in fact. At age 59, Meitner left Germany forever with 10 marks in her purse, one small suitcase, and a diamond ring given to her by Otto Hahn that he had inherited from his mother.

    This talk will be a combination of facts, excerpts from the film, "Path to Nuclear Fission: The Story of Lise Meitner and Otto Hahn" (a film by Rosemarie Reed), and personal stories heard from my father, aunts, and uncles. Lise Meitner’s early years, her role in the discovery of nuclear fission, her escape from Germany, and the consequences that followed will be covered.

March 15 — "Epidemics, Erdos numbers, and the Internet: The Physics of Networks"

  • Presenter: Mark Newman, University of Michigan
  • Host: Leo Radzihovsky
  • Abstract: There are networks in every part of our lives: the Internet, the road network, networks of friendship or acquaintance, biochemical networks, ecological networks, the power grid, and many others. As large-scale data on these networks has become available in the last few years, a new science of networks has grown up combining observations and theory to shed light on systems ranging from bacteria to the whole of human society.  This talk will give an introduction to this rapidly-growing field, and explain some its best known results and how physics and physical methods can contribute to their understanding.

March 22 — "Programmable control of indistinguishable particles: from sampling to clocks to qubits"

  • Presenter: Adam Kaufman, JILA, University of Colorado, Boulder
  • Host: Leo Radzihovsky
  • Abstract: Quantum information science seeks to exploit the collective behavior of a large quantum system to enable tasks that are impossible (or less possible!) with classical resources alone. While this burgeoning field encompasses a variety of goals, ranging from metrology to computing, most of them rely on the preparation and control of many identical particles or qubits. Meeting this need is a defining challenge of the field. There are several promising platforms that are targeting these capabilities, and I will focus on one such platform — optically-trapped neutral atoms. We have been developing a new suite of tools, based on the use of more exotic atomic species, new trapping architectures, and new control methods. I will provide an overview of these developments and a few specific examples of our recent results, including the use of atoms as indistinguishable bosons for sampling problems, a new kind of atomic clock, and a different kind of qubit.

March 29 — No Colloquium, Spring Break 

April 5 — "Fast jet stream winds get faster under climate change"

  • Presenter: Tiffany Shaw, University of Chicago
  • Host: Michael Ritzwoller
  • Abstract: Earth's upper-level jet streams influence the speed and direction of travel of weather systems and commercial aircraft. The fastest jet stream winds are also linked to severe weather occurrence. Climate change is known to accelerate the average speed of the jet stream. However, little is known about how the fastest jet stream winds will change. Here we show fast jet stream winds get faster under climate change using daily data from climate model projections across a hierarchy of physical complexity. The fastest winds also increase substantially more than the average winds. We give a physical basis for why fast winds get faster and show it follows from the moist get moister response under climate change. The results show moist thermodynamics can explain projected future changes in commercial flight times and clear-air turbulence, including a potential increase in severe weather occurrence under climate change.

April 12 — "From quantum optics to bits and pieces"

  • Presenter: Klaus Mølmer, Niels Bohr Institute, University of Copenhagen
  • Host: Jun Ye and Ana Maria Rey
  • Abstract: In this talk, I shall review the arguments applied by Roy Glauber in the early 1960’s to characterize temporal fluctuations in photo-detection signals.  Such fluctuations can be signatures of non-classical properties, and the theory of photo-detection gave rise to the field of quantum optics with visions to control atomic light emitters to prepare and apply a variety of quantum states of light in experiments. In the past decades, bits and pieces of solid-state materials were manufactured with high purity and precision, enabling observation of similar phenomena with superconducting circuits, microwaves and acoustic waves as had been studied with single atoms and photons in quantum optics. 

    As a theorist I have worked with methods that refine and elaborate on Glauber’s theories to describe the dynamics of open quantum systems, i.e., systems subject to interactions with their environment. I will show how these methods reintroduce, but with a plot twist, Niels Bohr’s quantum jumps in modern quantum physics. They provide the ultimate data processing tools for precision metrology, they offer unique insights into the dynamics of quantum systems, and they imply delightful encounters with the famous discussions between Niels Bohr and Albert Einstein on the interpretation of quantum theory.

April 19 — "The Fascinating History of Numbers in Ancient Mesopotamia"

  • Presenter: Jeanne Nijhowne, University of Colorado, Boulder
  • Host: Paul Beale
  • Abstract: For tens of thousands of years, humans got along perfectly well without numbers as we understand them. Then around 5000 years ago for reasons that remain unclear, people in the ancient Near East began living in cities with monumental architecture, civil and religious bureaucracies, centralized food distribution systems, and long-distance trading networks. It was simply not possible to run such complex societies without some kind of accounting system or knowledge of mathematical principles. This lecture concentrates on the long, and dare I say “tortured” history of Mesopotamian counting systems. The developments in numbers and mathematics will be discussed in their cultural context in an effort to explain why changes happened as they did and their legacy still influencing us today.
    Jeanne Nijhowne holds a Ph.D. in Anthropology with a specialty in the archaeology of the ancient Near East. She has worked on archaeological excavations in Egypt, Iraq, Turkey, Jordan and Syria ranging in time from the 8th millennium B.C. to the 4th century A.D. She currently works as the Graduate Program Assistant in the Department of Physics and teaches a summer class on Mesopotamian archaeology for the Anthropology Department at CU.

April 26 — "A diatomic molecule in a superfluid helium droplet: Is the anomalous Zeeman splitting a signature of a microscopic Einstein - de Hass effect?"

  • Presenter: Gary Douberly, University of Georgia
  • Host: Heather Lewandowski
  • Abstract: The first beam of helium droplets was reported in the 1961 paper Strahlen aus kondensiertem Helium im Hochvakuum by Von E. W. Becker and co-workers [1]. However, molecular spectroscopy of helium-solvated dopants wasn't realized until 30 years later in the laboratories of Scoles and Toennies [2,3].
    It has now been over two decades since this early, seminal work on doped helium droplets, yet the field of helium droplet spectroscopy is still fresh with vast potential. Analogous in many ways to cryogenic matrix isolation spectroscopy, the helium droplet is an ideal environment to spectroscopically probe difficult to prepare molecular species, such as radicals, carbenes and ions. The quantum nature of helium at 0.35 K often results in molecular spectra that are sufficiently resolved to evoke an analysis of line shapes and fine-structure that demands rigorous “effective Hamiltonian” treatments, revealing the microscopic details associated with the interaction between the molecular dopant and the superfluid solvent environment. This lecture will focus on our successful attempts to dope the hydroxyl radical (OH) and hydroxyl-containing molecular complexes into helium droplets [4,5,6]. The properties of these systems have been probed with infrared laser spectroscopy. Anomalous effects such as an unusually large Zeeman splitting are interpreted with a model that accounts for angular momentum transfer between dopant and solvent, which is akin to a microscopic Einstein – de Hass effect.
    [1]  E. W. Becker, R. Klingelhöfer, P. Lohse, Z. Naturforsch. A 16A, 1259 (1961).
    [2]  S. Goyal, D. L. Schutt, G. Scoles, Phys. Rev. Lett. 69, 933 (1992).
    [3]  M. Hartmann, R. E. Miller, J. P. Toennies, A. F. Vilesov, Phys. Rev. Lett. 75, 1566 (1995).
    [4]  Raston, P.L.; Liang, T.; Douberly, G.E., “Anomalous -doubling in the infrared spectrum of the hydroxyl radical in helium nanodroplets” Journal of Physical Chemistry A 117, 8103-8110 (2013).
    [5]  Brice, J.T.; Liang, T.; Raston, P.L.; McCoy, A.B.; Douberly, G.E. “Infrared Stark and Zeeman spectroscopy of OH-CO: The entrance channel complex along the OH + CO →  trans-HOCO reaction pathway” Journal of Chemical Physics 145, 124310 (2016).
    [6]  Raston, P.L; Obi, E.I.; Douberly, G.E. “Infrared Spectroscopy of the Entrance Channel Complex Formed Between the Hydroxyl Radical and Methane in Helium Nanodroplets” Journal of Physical Chemistry A 121, 7597-7602 (2017).


May 3 — "Spinning top-ology"

  • Presenter: William Irvine, University of Chicago
  • Host: Leo Radzihovsky
  • Abstract: Geometry, topology and broken symmetry play a powerful role in determining the physics of materials. In this colloquium I will present experimental realizations of activated materials and fluids built out of mechanically spinning components and show how the subtle interplay of structure, time-reversal and parity leads to `odd' solid and fluid mechanics. The self-assembled chiral phases we observe blur the boundary between solids and fluids spontaneously exhibiting novel phenomena both fluid and solid: from chiral surface waves to odd instabilities and motile topological defects. The simple addition of transverse interactions through rotational drive in the 'atomic' constituents proves to be a powerful twist: spontaneously endowing these materials with their active dynamics and exotic responses such as odd viscosity and odd elasticity.

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