Past Events

  • Condensed Matter seminar: "Exploring the Landscape of Complex Quantum States: From New Phases of Matter to Robust Schemes for Quantum Computation"

    David Rittenhouse Laboratory, A4

    Ksheerasagar "Sagar" Vijay, Harvard University

    We present recent advances in our understanding of (i) exotic quantum phases of matter in three dimensions, and (ii) robust mechanisms for storing and processing quantum information, that have been enabled by new techniques to study highly-entangled quantum states.  First, we introduce fundamentally new kinds of gapped quantum phases in three spatial dimensions, which are characterized by the presence of point-like excitations that are strictly immobile at zero temperature, and by degenerate ground-states that are locally indistinguishable.

  • Condensed Matter seminar: "Tensor Gauge Theories of Fractons"

    David Rittenhouse Laboratory, A4

    Michael Pretko, University of Colorado

    A fracton is an unusual new type of emergent quasiparticle, first proposed in the context of quantum spin liquids, which does not have the ability to move by itself.  Rather, fractons can only move by forming certain bound states.  In this talk, I will show that symmetric tensor gauge theories provide a natural theoretical framework for fractons, with the unusual mobility restrictions encoded in a set of higher moment charge conservation laws, such as conservation of dipole moment.  I will then show how the tensor gauge theory formalism identifies the conventional ela

  • Astronomy seminar: "Distances for Cosmology"

    David Rittenhouse Laboratory, A2

    Rachael Beaton, Princeton/Carnegie

    Distances are the fundamental datum by which we translate observational quantities into astrophysical ones and distances remain difficult to measure. I will describe techniques that use old stellar populations in galaxies to determine distances because old stellar populations exist in all galaxies of all hubble types, in each structural component of a galaxy, and are observable regardless of the galaxy's orientation. Thus, old stellar populations provide a means of reaching galaxies and galaxy structures that are not feasible via the classical Cepheid-based distance ladder.

  • High Energy Theory seminar: "Shift Symmetries in (A)dS"

    David Rittenhouse Laboratory, 2N36

    Kurt Hinterbichler, Case Western Reserve University

    I will discuss the generalizations of shift symmetries, galileon symmetries, and extended galileon symmetries to (A)dS space and to higher spin.   Unlike flat space, these symmetries are present only for particles with particular masses, and are related to partially massless symmetries.  For the case of scalars, I will discuss non-linear extensions of the symmetries and invariant interactions. This leads to a unique ghost-free theory in (A)dS space that is an (A)dS extension of the special Galileon.

  • Condensed Matter seminar: "The Berry curvature dipole of metals and the crossover from composite fermions to exciton superfluid”

    David Rittenhouse Laboratory, A4

    Inti Sodemann-Villadiego, Max Planck Institute, Dresden

    The first part of this talk will summarise our progress in non-linear transport of metals. I will describe a non-linear Hall effect that is allowed by time reversal symmetry and is controlled by the "Berry curvature dipole” (the average of the Berry curvature gradient in momentum space). I will argue that such Berry curvature dipole offers a solution to the old problem of defining an “order parameter” for broken inversion symmetry in metals, by playing the role of a non-linear version of the Drude weight.

  • Condensed Matter seminar: "Dirty Quantum Magnets"

    David Rittenhouse Laboratory, A4

    Itamar Kimchi, University of Colorado

    Studying quantum entanglement over the past 1--2 decades has allowed us to make remarkable theoretical progress in understanding correlated many-body quantum systems. However electrons in real materials experience random heterogeneities ("dirt") whose theoretical treatment, including strong correlations, has been a challenge.

  • Condensed Matter Seminar: "Revisiting and Repurposing the Double Helix"

    David Rittenhouse Laboratory, A6

    Taekjip Ha, Johns Hopkins University

    DNA is an iconic molecule that forms a double helical structure, providing the basis for genetic inheritance, and its physical properties have been studied for decades. In this talk, I will present evidence that sequence and methylation dependent physical properties of DNA such as flexibility and self-association may be important for biological functions [1, 2]. In addition, I will present a new application of DNA where mechanical modulations of cell behavior can be studied at the single molecule level using rupturable DNA tethers [3].

  • Particle Physics seminar: "First results from the PROSPECT reactor neutrino experiment"

    David Rittenhouse Laboratory, 4N12

    Danielle Norcini, Yale University

    Experiments at nuclear reactors have played a key role in determining the properties of the weakly-interacting neutrinos. Results from recent reactor experiments suggest a disagreement between the observed antineutrino flux and energy spectrum when compared to predictions. Beyond the Standard Model sterile neutrinos and corrections to complex nuclear models have been posed to explain the discrepancy. To address this physics, the PROSPECT experiment precisely measures antineutrino energy spectra at multiple, very short baselines (< 10m) from the High Flux Isotope Reactor.

  • High Energy Theory seminar: "Axion couplings and implications for cosmology and astrophysics"

    David Rittenhouse Laboratory, 2N36

    JiJi Fan, Brown University

    Many cosmological models rely on large couplings of axions (pseudo-scalar fields) to gauge fields. Examples include theories of magnetogenesis, inflation on a steep potential, chiral gravitational waves, and chromonatural inflation.

  • Penn Science Cafe: "The Physics of Foam"

    Suzanne Roberts Theater, 2nd Floor Lobby, 480 South Broad Street, Philadelphia

    Douglas Durian, University of Pennsylvania

    It's easy to foam up soapy water but not to understand the surprising properties of foam. How can it be white and solid when it's made mostly of gas and a little liquid, neither of which is white or solid? Douglas Durian will explain how foams change over time and some of the excitement they offer as a modern research topic in fundamental physics and mathematics.