Aspen Center for Physics

2022 Colloquia

Thursdays at 3 p.m. MDT, 9 p.m. UTC

Click Here To Access the Zoom Talks

  • June 2
    Fundamental Physics from Galaxy Surveys
    Speaker: Mikhail Ivanov,  Institute for Advanced Study
    The distribution of galaxies on large scales is a sensitive probe of cosmological physics. In particular, the structure of this distribution depends on properties of dark matter and the dynamics of the early universe. Understanding this dependence, however, is a challenging task because the observed galaxy distribution is modulated by a variety of non-linear effects. I will present innovative theoretical tools that have allowed for a systematic analytic description of these effects. These tools play a central role in a new program of extracting cosmological information from galaxy surveys. I will share some results of this program from my independent analysis of the public data from the Baryon acoustic Oscillation Spectroscopic Survey. These results include the measurement of the Hubble constant as well as constraints on new physics and the early Universe. Finally, I will discuss the main challenges of this program and possible synergies with machine learning.
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  • June 9
    Accelerating first-principles calculations of the structure of matter with machine learning
    Speaker: Phiala Shanahan, MIT
    Our understanding of the structure of matter, encapsulated in the Standard Model of particle physics, is that protons, neutrons, and nuclei emerge dynamically from the interactions of underlying quark and gluon degrees of freedom. I will describe recent progress in first-principles studies of the Standard Model, highlighting first direct studies of nuclear structure and interactions, including calculations relevant to the interpretation of dark matter direct detection experiments. Motivated by the extreme computational demands of such studies at the nuclear scale, I will discuss opportunities for acceleration through provably-exact machine learning algorithms.
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  • June 16
    Machine learning for biological sequence design with therapeutic applications
    Speaker: Lucy Colwell, Cambridge University
    Prediction of protein function from sequence is a central challenge that allows us to discover new proteins with specific functional properties. Experimental and computational labels can be used to train and validate machine learning models that predict protein function directly from sequence. I will present deep learning models that accurately predict the presence and location of functional domains within protein sequences, adding hundreds of millions of annotations to public databases. Furthermore, experimental breakthroughs enable data on the relationship between sequence and function to be rapidly acquired. However, the cost and latency of wet-lab experiments require methods that find good sequences in few experimental rounds, where each round contains large batches of sequence designs. In this setting, I will discuss model-based optimization approaches that take advantage of sample inefficient methods to find diverse sequence candidates for experimental evaluation. The potential of this approach is illustrated through the design and experimental validation of proteins and peptides for therapeutic applications.
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  • June 23
    LIGO: a 1/10 scale model of Cosmic Explorer
    Speaker: David Shoemaker, MIT Kavli Institute
       The field of gravitational-wave astronomy has demonstrated its ability to provide insights into gravitation in the extremes of nature, as well as its ability to complement photon and particle astronomy and astrophysics. With roughly 100 events since the first observation in 2015, the approach to the instrumentation and its ability to deliver more science when upgraded even incrementally is demonstrated.
        The field is now formulating observatory concepts for a significant step in sensitivity – ten times that of the current instruments. This will bring to the order of 103 more sources into reach, in addition to improving the resolution for nearby sources and increasing the sensitive range in frequency and thus variety of sources.
        We will describe the US vision for the next generation gravitational-wave observatory, Cosmic Explorer, and call on the experience to date with LIGO to provide a sense of the feasibility and the path to realization for this major undertaking.
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  • June 30
    How Materials Can Learn How to Function
    Speaker: Andrea Liu, University of Pennsylvania
  • Artificial neural networks learn via optimization where a loss function is minimized by a computer to achieve the desired result. But physical networks, such as mechanical spring networks or flow networks, have no attached processors to perform the optimization, so they cannot minimize such a loss function. What such systems do automatically minimize is their elastic energy (mechanical networks) or the dissipated power (flow network). I will describe how these natural physical processes can be harnessed to teach systems how to perform machine learning tasks such as classification, as well as functions inspired by biology. For example, the ability of proteins (e.g. hemoglobin) to change their conformations upon binding of an atom (oxygen) or molecule, or the ability of the brain’s vascular network to send enhanced blood flow and oxygen to specific areas of the brain associated with a given task. This learning strategy has recently been implemented in electrical circuits.
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  • July 7
    New Rules: Quantum Circuits, Cellular Automata, Complexity and Chaos
    Speaker: Austen Lamacraft, University of Cambridge
  • Many of you will have played with cellular automata such as Conway's Game of Life. These are model systems in which complex and chaotic behaviors emerge from simple dynamical rules.

    Motivated by quantum computation, physicists have in recent years begun to study quantum circuits, which are in some way a quantum analogue of cellular automata. In this talk, I'll discuss some of the similarities and differences between these two classes of systems, and what they can teach us about classical and quantum dynamics more generally.
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  • July 14
    Monitoring Quantum Dynamics
    Speaker: Matthew P.A. Fisher, University of California Santa Barbara
    When a quantum system is coupled to a dissipative environment an initially pure state becomes rapidly mixed as information is lost, and classical behavior invariably follows. Recently, another type of open system dynamics has been explored, when a quantum system is continuously \mon-
    itored" by an observer, making a sequence of measurements, and a pure quantum state remains pure. The resulting quantum trajectories constitute an ensemble of pure states, which can (in principle) be experimentally accessed in digital quantum simulators. In the many-body context, these quantum trajectories can have a rich entanglement structure, exhibiting - for example - dynamical phase transitions between volume law and area law entanglement, and between phases with or without symmetry breaking and/or topological order. For mixed initial density matrices, monitoring can lead to a plethora of puri cation transitions, and reveals underlying connections with quantum encoding. Accessing such physics in the lab is challenged by the need for post-selection, which might be circumnavigated by decoding using active error correction. In this talk I will try to give an overview of some topics in such monitored quantum dynamics.
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  • July 21
    Using the Solar Wind as a Natural Laboratory to Study Space Plasma Turbulence
    Speaker: Kristopher Klein, University of Arizona
    Turbulent magnetic and velocity fluctuations are responsible for the transport of mass, momentum, and energy in a variety of plasma systems throughout the solar system and universe. In this talk, I discuss recent advances in our understanding of the role that turbulence plays in weakly collisional plasma systems drawn from in situ measurements of electromagnetic fields and charged particle velocity distributions from the Sun's extended atmosphere, made over the last half-century, including most recently by Parker Solar Probe and MMS. Changes in the nature of the turbulence with varying distance from the Sun's surface, as well as a function of key dimensionless system parameters, are discussed. We conclude with open questions regarding the three-dimensional structure and dynamics of plasma turbulence that will be addressed over this next decade by multi-point, multi-scale missions such as the recently selected HelioSwarm Observatory. 
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  • July 28
    Probing Dense Matter with Neutron Star Mergers
    Speaker: Carolyn Raithel, Institute for Advanced Study
  • Neutron stars provide a unique laboratory for studying the properties and interactions of ultra-dense matter. With the recent advent of gravitational wave astronomy, we have gained a new window into the extreme conditions that characterize the neutron star interior. In this talk, I will discuss what we have learned so far about the dense-matter equation of state (EOS) from the first observations of inspiraling neutron stars. I will then present a set of numerical merger simulations that use a phenomenological framework to study new parts of the EOS parameter space. Using these simulations, I will discuss the additional physics that we might be able to probe with a future measurement of post-merger gravitational waves, which are emitted by the hot and massive neutron star remnant that forms following the merger. The conditions of the post-merger phase differ significantly from the inspiral, providing the possibility of constraining the EOS across a range of densities and temperatures.
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  • August 4
    Strong Electronic Correlations, Topological Phases and Unconventional Superconductivity in Magical Flatbands
    Speaker: Ali Yazdani, Princeton University
  • One the exciting new material platforms for exploring properties of highly interacting electrons is the newly discovered bilayers of graphene twisted to a magic angle. I will describe how using high resolution experiments with the scanning tunneling microscope, we can explore the remarkably complex physics of this novel system. I will show how we characterize strong electronic correlations, how correlations in this system created novel topological phases and describe how we probe the nature of superconductivity that emerges in this material in the presence of strong electronic correlation. I will show the remarkable similarity in the properties of the superconducting phase in this material and that which occurs in high-Tc cuprate superconductors.
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  • August 11
    Exotic Superconductivity in Graphene Multilayers
    Speaker: Erez Berg, Weizmann Institute of Science
    Recently, graphene multilayers have emerged as a rich platform to study quantum many-body physics. I will describe recent experiments on a stack of three layers of graphene, where superconductivity was recently discovered at the boundary between states with different broken symmetries. Experiments hint to an unconventional mechanism for superconductivity, where counterintuitively, the binding of electrons into pairs originates from the repulsive Coulomb interaction between them. Even more interestingly, one of the superconducting phases in trilayer graphene seems to be an unusual fully spin polarized triplet state. The topology of its order parameter space, that intertwines the phase of the superconducting condensate with the spin polarization, can lead to unusual phenomena, such as anomalous supercurrent dissipation and a fractional-period  ac Josephson effect.
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  • August 18
    The Central Dogma of Black Holes
    Speaker: Ahmed Almheiri, Institute for Advanced Study
  • Research over the past few decades has uncovered an intimate connection between gravity and quantum information and has led to surprising conclusions about the nature of black holes. In particular, it supports the so-called central dogma of black holes, the idea that a black hole behaves like a quantum system with a finite number of degrees of freedom that evolves under unitary but chaotic time evolution. I will motivate this picture of black holes and discuss how it follows from the path integral of gravity. Furthermore, I will highlight its implications on the information paradox regarding the fate of information that falls into a black hole, and on the more recent firewall paradox that puts into question the very existence of the black hole interior. We will see that progress on these questions is only possible because the path integral of gravity implements a quantum error correcting code.
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  • August 25
    Looking Beyond the Dark Matter in Axion Haloscopes
    Speaker: Nicholas Rodd, CERN
  • The coming decade will bring dramatic improvement in the axion dark-matter program as new experimental designs move beyond the proof of principle stage. In this talk I will outline two signals beyond dark matter that these instruments could discover. The first is a population of relativistic axions that were produced in the early universe and persist as a residual Cosmic axion Background (CaB). The second is high-frequency gravitational waves; I will outline how exploiting an analogy between axion and gravitational-wave electrodynamics allows for axion haloscopes to be converted into gravitational-wave telescopes.
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  • September 1
    Electroweak Baryogenesis and the LHC
    Speaker: Marcela Carena, Fermilab
  • With Run 3 of the LHC starting this summer, it is timely to take a fresh look at the question of whether the electroweak phase transition could have been the source of the observed matter-antimatter asymmetry of our universe. Such a process, known as electroweak baryogenesis, requires the existence of new particles related to the Higgs boson, new sources of CP violation, and possibly new forces, all manifesting during the electroweak phase transition in the early universe. I will discuss three examples of plausible scenarios, two focused on the problem of preserving an asymmetry once created, and the third exhibiting a new mechanism where the source of both CP violation and the resulting asymmetry comes from the dark matter sector.

  • September 8
    Anderson Transitions and (Lost) Conformal Invariance
    Speaker: Ilya Gruzberg, Ohio State University
    Anderson transitions (ATs) between metals and insulators or between topologically distinct insulators, share common features with conventional second-order phase transitions, such as the critical point of the Ising model for a magnet. However, ATs also exhibit many unusual features including the multifractal scaling of the critical wave functions. Conventional critical points possess conformal invariance which constrain their properties to the extent that they can be obtained exactly in two dimensions and to very high precision in three dimensions. Until recently, researchers assumed that Anderson transitions also possess conformal invariance and can be described by conformal field theories (CFTs). I will review recent progress in understanding the relation between conformal invariance and multifractal wave functions. The emerging picture puts serious doubt on the ability of CFTs to properly describe multifractality at ATs in both two and three dimensions.

  • September 15
    QFT Aspects of Symmetry
    Speaker: Ken Intriligator, University of California San Diego
  • Everything in the Universe, including the photons that we see and the quarks and electrons in our bodies, are actually ripples of quantum fields. Quantum field theory (QFT) is the underlying framework and examples include the most precisely tested theory in science, and also theories that remain full of mysteries.  QFT also describes condensed matter systems, connects (e.g. via AdS/CFT) to string theory and quantum gravity, describes inflationary cosmology, and has fruitful interconnections with mathematics.  Symmetry has deep and powerful realizations and implications throughout physics, and this is especially so for the study of QFT and its renormalization group flows (zooming out). Topological QFTs (TQFTs) have been under intense study, including in the context of condensed matter systems and also mathematics, and also play roles in non-topological QFTs.  There has been great recent synergy and progress in generalized notions of symmetries and applications to QFT; our current Aspen workshop is devoted to these topics. I will try to provide an accessible, colloquium-level introduction to aspects of symmetries and QFT, both old and new.