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Speaker: Maria Tikhanovskaya (Harvard)Title: Maximal quantum chaos of the critical Fermi surfaceVenue: VirtualSpeaker: Maria Tikhanovskaya (Harvard) Title: Maximal quantum chaos of the critical Fermi surface Abstract: In this talk, I will describe many-body quantum chaos in a recently proposed large-N theory for critical Fermi surfaces in two spatial dimensions, by computing out-of-time-order correlation functions. I will use the ladder identity proposed by Gu and Kitaev, and show that the chaos Lyapunov exponent in this system takes on the maximum possible value of 2πkBT/ℏ, where T is the absolute temperature. In addition, by varying the dynamic critical exponent, I will show that the maximal chaos persists only in the regime where quasiparticles are absent. When quasiparticles are present, the Lyapunov exponent scales with the temperature as ~ T^a, where a < 1, which… |
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Speaker:Title: Metals with strongly correlated electrons: quantum criticality, disordered interactions, Planckian dissipation, and scale invarianceVenue: VirtualSpeaker: Aavishkar Patel (UC Berkeley) Title: Metals with strongly correlated electrons: quantum criticality, disordered interactions, Planckian dissipation, and scale invariance Abstract: Metals that do not fit Landau’s famous Fermi liquid paradigm of quasiparticles are plentiful in experiments, but constructing their theoretical description is a major challenge in modern quantum many-body physics. I will describe new models that can systematically describe such non-Fermi liquid metals at quantum critical points, and that allow for the accurate computation of a whole host of experimentally measurable static and dynamic quantities despite the presence of both strong correlations and disorder. I will further demonstrate that disorder coupling to interaction operators can lead to the experimentally observed linear-in-temperature (T-linear) resistivity seen at metallic quantum… |
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Speaker: Lukasz Fidkowski (U Washington)Title: Gravitational anomaly of 3 + 1 dimensional Z2 toric code with fermionic charges and ferionic loop self-statisticsVenue: VirtualSpeaker: Lukasz Fidkowski (U Washington) Title: Gravitational anomaly of 3 + 1 dimensional Z2 toric code with fermionic charges and ferionic loop self-statistics Abstract: Quasiparticle excitations in 3 + 1 dimensions can be either bosons or fermions. In this work, we introduce the notion of fermionic loop excitations in 3 + 1 dimensional topological phases. Specifically, we construct a new many-body lattice invariant of gapped Hamiltonians, the loop self-statistics μ = ±1, that distinguishes two bosonic topological orders that both superficially resemble 3 + 1d Z2 gauge theory coupled to fermionic charged matter. The first has fermionic charges and bosonic Z2 gauge flux loops (FcBl) and is just the ordinary fermionic toric code. The second has fermionic charges and fermionic… |
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Speaker: Fei Yan (Rutgers)Title: Defects, link invariants and exact WKBVenue: virtualSpeaker: Fei Yan (Rutgers) Title: Defects, link invariants and exact WKB Abstract: I will describe some of my recent work on defects in supersymmetric field theories. The first part of my talk is focused on line defects in certain large classes of 4d N=2 theories and 3d N=2 theories. I will describe geometric methods to compute the ground states spectrum of the bulk-defect system, as well as implications on the construction of link invariants. In the second part I will talk about some perspectives of surface defects in 4d N=2 theories and related applications on the exact WKB method for ordinary differential equations. This talk is based on past joint work with A. Neitzke, various work in progress with D…. |
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Speaker: Daniel Harlow (MIT)Title: Symmetry in quantum field theory and quantum gravity 2Venue: VirtualSpeaker: Daniel Harlow (MIT) Title: Symmetry in quantum field theory and quantum gravity 2 Abstract: In this talk I will give an overview of semi-recent work with Hirosi Ooguri arguing that three old conjectures about symmetry in quantum gravity are true in the AdS/CFT correspondence. These conjectures are 1) that there are no global symmetries in quantum gravity, 2) that dynamical objects transforming in all irreducible representations of any gauge symmetry must exist, and 3) all internal gauge symmetries must be compact. Along the way I will need to carefully define what we mean by gauge and global symmetries in quantum field theory and quantum gravity, which leads to interesting applications in various related fields. These definitions will… |
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Speaker:Title: Symmetry in quantum field theory and quantum gravity 1Venue: VirtualSpeaker: Daniel Harlow (MIT) Title: Symmetry in quantum field theory and quantum gravity 1 Abstract: In this talk I will give an overview of semi-recent work with Hirosi Ooguri arguing that three old conjectures about symmetry in quantum gravity are true in the AdS/CFT correspondence. These conjectures are 1) that there are no global symmetries in quantum gravity, 2) that dynamical objects transforming in all irreducible representations of any gauge symmetry must exist, and 3) all internal gauge symmetries must be compact. Along the way I will need to carefully define what we mean by gauge and global symmetries in quantum field theory and quantum gravity, which leads to interesting applications in various related fields. These definitions will be… |
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Speaker: Shinsei Ryu (Princeton University)Title: Multipartitioning topological phases and quantum entanglementVenue: virtualSpeaker: Shinsei Ryu (Princeton University) Title: Multipartitioning topological phases and quantum entanglement Abstract: We discuss multipartitions of the gapped ground states of (2+1)-dimensional topological liquids into three (or more) spatial regions that are adjacent to each other and meet at points. By considering the reduced density matrix obtained by tracing over a subset of the regions, we compute various correlation measures, such as entanglement negativity, reflected entropy, and associated spectra. We utilize the bulk-boundary correspondence to achieve such multipartitions and construct the reduced density matrix near the entangling boundaries. We find the fingerprints of topological liquid in these quantities, such as (universal pieces in) the scaling of the entanglement negativity, and a non-trivial distribution of the spectrum of the partially… |
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Speaker: B. Andrei Bernevig (Princeton University)Title: Exact Eigenstates in Non-Integrable Systems: A violation of the ETHVenue: virtualSpeaker: B. Andrei Bernevig (Princeton University) Title: Exact Eigenstates in Non-Integrable Systems: A violation of the ETH Abstract: We find that several non-integrable systems exhibit some exact eigenstates that span the energy spectrum from lowest to the highest state. In the AKLT Hamiltonian and in several others “special” non-integrable models, we are able to obtain the analytic expression of states exactly and to compute their entanglement spectrum and entropy to show that they violate the eigenstate thermalization hypothesis. This represented the first example of ETH violation in a non-integrable system; these types of states have gained notoriety since then as quantum Scars in the context of Rydberg atoms experiments. We furthermore show that the structure of these states, in most… |
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Speaker:Title: Quantum Geometric Aspects of Chiral Twisted Graphene ModelsVenue: virtualSpeaker: Jie Wang (Simons Foundation) Title: Quantum Geometric Aspects of Chiral Twisted Graphene Models Abstract: “Moire” materials produced by stacking monolayers with small relative twist angles are of intense current interest for the range of correlated electron phenomena they exhibit. The quench of the kinetic energy means that the interacting physics is controlled by the interplay between the interaction scale and intrinsic quantum geometries of the flat band states, in particular the Berry curvature and the Fubini-Study metric, which are in general spatially non-uniform. We show that the analytical solution of the twisted bilayer graphene wavefunction in the chiral limit has a special band geometry, endowing the Brillouin zone with a complex structure. This talk focus on the origin of… |
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Speaker: Jeongwan Haah (Microsoft)Title: A degeneracy bound for homogeneous topological orderVenue: virtualSpeaker: Jeongwan Haah (Microsoft) Title: A degeneracy bound for homogeneous topological order |
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Speaker: Yifan Wang (NYU)Title: Fusion Category Symmetries in Quantum Field TheoryVenue: virtualSpeaker: Yifan Wang (NYU) Title: Fusion Category Symmetries in Quantum Field Theory Abstract: Topological defects provide a modern perspective on symmetries in quantum field theory. They generalize the familiar inverti ble symmetries described by groups to non-invertible symmetries described by fusion categories. Such generalized symmetries are ubiquitous in quantum field theory and provide new constraints on renormalization group flows and the IR phase diagram. In this talk I’ll review some recent progress in identifying and understanding fusion category symmetries in 1+1d conformal field theories. Time permitting, I’ll also comment on higher dimensional generalizations. |
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Speaker: Clay Cordova (U Chicago)Title: Non-Invertible Duality Defects in 3+1 DimensionsVenue: virtualSpeaker: Clay Cordova (U Chicago) Title: Non-Invertible Duality Defects in 3+1 Dimensions Abstract: For any quantum system invariant under gauging a higher-form global symmetry, we construct a non-invertible topological defect by gauging in only half of spacetime. This generalizes the Kramers-Wannier duality line in 1+1 dimensions to higher spacetime dimensions. We focus on the case of a one-form symmetry in 3+1 dimensions and determine the fusion rule. From modular invariance and a direct analysis of one-form symmetry-protected topological phases, we show that the existence of certain kinds of duality defects is intrinsically incompatible with a trivially gapped phase. By further assuming time-reversal symmetry, we find that the presence of certain duality defects implies that the low-energy phase has to be… |
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Speaker: Eric Sharpe (Virginia Tech)Title: Anomaly resolution via decompositionVenue: virtualSpeaker: Eric Sharpe (Virginia Tech) Title: Anomaly resolution via decomposition Abstract: In this talk we will discuss a method of anomaly resolution due to Wang-Wen-Witten in the special case of (1+1) dimensional theories. Briefly, for our purposes, Wang-Wen-Witten argued that an ill-defined anomalous orbifold [X/G] could be resolved by extending G to a larger group and adding suitable phases. We analyze this process from the perspective of decomposition, a property of (1+1)-dimensional theories with “one-form symmetries” first described in 2006. Examples of such theories include orbifolds with trivially-acting subgroups, of which the extensions of [X/G] are examples. After a review of decomposition, we will see that decomposition implies that in (1+1) dimensions, the Wang-Wen-Witten procedure results in orbifolds… |
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Speaker: Biao Lian (Princeton)Title: Integrability and chaos of 1+1d chiral edge statesVenue: VirtualSpeaker: Biao Lian (Princeton) Title: Integrability and chaos of 1+1d chiral edge states Abstract: I will talk about the integrability and chaos of 1+1d interacting chiral edge states, which may arise on the edge of 2+1d topological phases. We show that integrable chiral Luttinger liquid is not always a good low energy description of the edge states, and marginal interactions can significantly affect their spectrum and integrability. We first study N identical chiral Majorana fermion modes with random 4-fermion interactions, where we show that the system undergoes a transition from integrable to quantum chaotic as N increases. The large N limit defines a chiral SYK model where the Lyapunov exponent in the out-of-time-ordered correlation can be solved analytically…. |
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Speaker: Anton Kapustin (Caltech)Title: Electric-magnetic duality and the Geometric Langlands dualityVenue: virtualTitle: Electric-magnetic duality and the Geometric Langlands duality Abstract: I will give a pedagogical review of the connection between electric-magnetic duality and the Geometric Langlands duality. |