|
Speaker: Guanyu ZhuTitle: Fault-tolerant quantum computation via topological order on fractals and emergent symmetriesVenue: Hybrid- G10Quantum Matter Seminar Speaker: Guanyu Zhu (IBM Quantum, T. J. Watson Research Center) Title: Fault-tolerant quantum computation via topological order on fractals and emergent symmetries Abstract: Topological quantum error correcting codes in integer spatial dimensions have been widely studied in the field of quantum information. A remaining major challenge is to reduce the space-time overhead for universal fault-tolerant quantum computation with topological codes. In the first part of my talk, I will present a theory of topological order and quantum codes on fractals embedded in three and higher dimensions and its connection to systolic geometry. The construction of such fractal codes can hence significantly reduce the space overhead. In the second part, I will show how to perform… |
|
Speaker: Nishad MaskaraTitle: Enhancing Detection of Topological Order by Local Error CorrectionVenue: CMSA Room G10Quantum Matter Seminar Speaker: Nishad Maskara (Harvard) Title: Enhancing Detection of Topological Order by Local Error Correction Abstract: The exploration of topologically-ordered states of matter is a long-standing goal at the interface of several subfields of the physical sciences. Such states feature intriguing physical properties such as long-range entanglement, emergent gauge fields and non-local correlations, and can aid in realization of scalable fault-tolerant quantum computation. However, these same features also make creation, detection, and characterization of topologically-ordered states particularly challenging. Motivated by recent experimental demonstrations, we introduce a new paradigm for quantifying topological states—locally error-corrected decoration (LED)—by combining methods of error correction with ideas of renormalization-group flow. Our approach allows for efficient and robust identification of topological order, and is… |
|
Speaker: Abijith KrishnanTitle: A Plane Defect in the 3d O(N) ModelVenue: HybridQuantum Matter Seminar Speaker: Abijith Krishnan (MIT) Title: A Plane Defect in the 3d O(N) Model Abstract: It was recently found that the classical 3d O(N) model in the semi-infinite geometry can exhibit an “extraordinary-log” boundary universality class, where the spin-spin correlation function on the boundary falls off as (log x)^(-q). This universality class exists for a range 2≤N<Nc and Monte-Carlo simulations and conformal bootstrap indicate Nc>3. In this talk, I’ll extend this result to the 3d O(N) model in an infinite geometry with a plane defect. I’ll explain using the renormalization group (RG) that the extraordinary-log universality class is present for any finite N≥2, and that a line of defect fixed points is present at N=∞. This line… |
|
Speaker: Alexander ZlokapaTitle: Traversable wormhole dynamics on a quantum processorVenue: Hybrid- G10Quantum Matter Seminar Speaker: Alexander Zlokapa, MIT Title: Traversable wormhole dynamics on a quantum processor Abstract: The holographic principle, theorized to be a property of quantum gravity, postulates that the description of a volume of space can be encoded on a lower-dimensional boundary. The anti-de Sitter (AdS)/conformal field theory correspondence or duality is the principal example of holography. The Sachdev–Ye–Kitaev (SYK) model of N >> 1 Majorana fermions has features suggesting the existence of a gravitational dual in AdS2, and is a new realization of holography. We invoke the holographic correspondence of the SYK many-body system and gravity to probe the conjectured ER=EPR relation between entanglement and spacetime geometry through the traversable wormhole mechanism as implemented in the SYK model. A qubit can… |
|
Speaker: Andreas BauerTitle: Tensorial TQFT and disentangling modular Walker-Wang modelsVenue: CMSA Room G10Quantum Matter Seminar Speaker: Andreas Bauer (Freie Universität Berlin) Title: Tensorial TQFT and disentangling modular Walker-Wang models Abstract: I will introduce simple “tensorial” definitions for many algebraic and categorical structures appearing in the classification of topological phases of matter. Such “tensorial TQFTs” will be defined as maps that associate tensors to geometric/topological objects of some type, subject to gluing axioms. Tensorial TQFTs are very directly related to microscopic physical models in terms of discrete path integrals. I will use those tensorial definitions to construct invertible boundaries which disentangle modular Walker-Wang models. https://www.youtube.com/watch?v=MJ8NRSrvihQ&list=PL0NRmB0fnLJQAnYwkpt9PN2PBKx4rvdup&index=12 |
|
Speaker: Yichen HuangTitle: Quantum entropy thermalizationVenue: virtualQuantum Matter Seminar Speaker: Yichen Huang (Harvard) Title: Quantum entropy thermalization Abstract: In an isolated quantum many-body system undergoing unitary evolution, the entropy of a subsystem (smaller than half the system size) thermalizes if at long times, it is to leading order equal to the thermodynamic entropy of the subsystem at the same energy. We prove entropy thermalization for a nearly integrable Sachdev-Ye-Kitaev model initialized in a pure product state. The model is obtained by adding random all-to-all 4-body interactions as a perturbation to a random free-fermion model. In this model, there is a regime of “thermalization without eigenstate thermalization.” Thus, the eigenstate thermalization hypothesis is not a necessary condition for thermalization. References: arXiv:2302.10165, 2209.09826; Joint work with Aram W. Harrow… |
|
Speaker: Anna HasenfratzTitle: Strongly coupled ultraviolet fixed point and symmetric mass generation in four dimensions with 8 Kähler-Dirac fermionsVenue: virtualQuantum Matter Seminar Speaker: Anna Hasenfratz (University of Colorado) Title: Strongly coupled ultraviolet fixed point and symmetric mass generation in four dimensions with 8 Kähler-Dirac fermions Abstract: 4-dimensional gauge-fermion systems exhibit a quantum phase transition from a confining, chirally broken phase to a conformal phase as the number of fermions is increased. While the existence of the conformal phase is well established, very little is known about the nature of the phase transition or the strong coupling phase. Lattice QCD methods can predict the RG $\beta$ function, but the calculations are often limited by non-physical bulk phase transition that prevent exploring the strong coupling region of the phase diagram. Even the critical flavor number is controversial, estimates vary between $N_f=8$ and… |
|
Speaker: Rahul SahayTitle: Quantum Spin Lakes: NISQ-Era Spin Liquids from Non-Equilibrium DynamicsVenue: virtualQuantum Matter Seminar Speaker: Rahul Sahay (Harvard) Title: Quantum Spin Lakes: NISQ-Era Spin Liquids from Non-Equilibrium Dynamics Abstract: While many-body quantum systems can in principle host exotic quantum spin liquid (QSL) states, realizing them as ground states in experiments can be prohibitively difficult. In this talk, we show how non-equilibrium dynamics can provide a streamlined route toward creating QSLs. In particular, we show how a simple Hamiltonian parameter sweep can dynamically project out condensed anyons from a family of initial product states (e.g. dynamically “un-Higgs”), yielding a QSL-like state. We christen such states “quantum spin lakes” which, while not thermodynamically large QSLs, enable their study in NISQ-era quantum simulators. Indeed, we show that this mechanism sheds light on… |
|
Speaker: Ho Tat LamTitle: Non-invertible Symmetry Enforced GaplessnessVenue: virtualQuantum Matter Seminar Speaker: Ho Tat Lam (MIT) Title: Non-invertible Symmetry Enforced Gaplessness Abstract: Quantum systems in 3+1-dimensions that are invariant under gauging a one-form symmetry enjoy novel non-invertible duality symmetries encoded by topological defects. These symmetries are renormalization group invariants which constrain infrared dynamics. We show that such non-invertible symmetries often forbid a symmetry-preserving vacuum state with a gapped spectrum, leaving only two possibilities for the infrared dynamics: a gapless state or spontaneous breaking of the non-invertible symmetries. These non-invertible symmetries are realized in lattice gauge theories, which serve to illustrate our results. https://www.youtube.com/watch?v=A-47aZ4HS1k&list=PL0NRmB0fnLJQAnYwkpt9PN2PBKx4rvdup&index=16 |
|
Speaker: Han YanTitle: Fracton orders in hyperbolic space and its excitations with fractal mobilityVenue: virtualQuantum Matter Seminar Speaker: Han Yan (Rice U) Title: Fracton orders in hyperbolic space and its excitations with fractal mobility Abstract: Unlike ordinary topological quantum phases, fracton orders are intimately dependent on the underlying lattice geometry. In this work, we study a generalization of the X-cube model, on lattices embedded in a stack of hyperbolic planes. We demonstrate that for certain hyperbolic lattice tesselations, this model hosts a new kind of subdimensional particle, treeons, which can only move on a fractal-shaped subset of the lattice. Such an excitation only appears on hyperbolic geometries; on flat spaces, treeons become either a lineon or a planeon. Additionally, we find intriguingly that for certain hyperbolic tessellations, a fracton can be created… |
|
Speaker: Igor R. KlebanovTitle: Group Invariant States as Many-Body ScarsVenue: virtualQuantum Matter Seminar Title: Group Invariant States as Many-Body Scars Speaker: Igor R. Klebanov (Princeton University) Abstract: Quantum many-body scars have been an active area of research in Condensed Matter Physics for several years. In some many-body systems, the Hilbert space breaks up into a large ergodic sector and a much smaller scar subspace. It has been suggested [K. Pakrouski et al., Phys. Rev. Lett. 125 (2020) 230602] that the two sectors may be distinguished by their transformation properties under a large group whose rank grows with the system size (this group is not a symmetry of the Hamiltonian). The scars are invariant under this group, while all other states are not. We begin by reviewing some many-body… |
|
Speaker: Jacob McNamara (Caltech) and Matthew Reece (Harvard)Title: Reflections on Parity BreakingVenue: virtualQuantum Matter Seminar Speakers: Jacob McNamara (Caltech) and Matthew Reece (Harvard) Title: Reflections on Parity Breaking Abstract: One approach to the Strong CP Problem (known as Nelson-Barr models) is to assume that parity is a gauge symmetry, which is spontaneously broken in the world around us. In this talk, we will describe the formal meaning of parity as a gauge symmetry, and argue that the domain walls formed from spontaneous parity breaking are exactly stable. This stability can be understood as the result of an unusual sort of conserved charge, which has features in common with both gauge charges and global charges. We will explain how these charges are compatible with the expected absence of global symmetries in… |
|
Speaker: Yang QiTitle: Phase Fluctuations in Two-Dimensional Superconductors and Pseudogap PhenomenonVenue: virtualQuantum Matter Seminar Speaker: Yang Qi (Fudan) Title: Phase Fluctuations in Two-Dimensional Superconductors and Pseudogap Phenomenon Abstract: We study the phase fluctuations in the normal state of a general two-dimensional (2d) superconducting system with s-wave pairing. The effect of phase fluctuations of the pairing fields can be dealt with perturbatively using disorder averaging, after we treat the local superconducting order parameter as a static disordered background. It is then confirmed that the phase fluctuations above the 2d Berenzinskii-Kosterlitz-Thouless (BKT) transition give birth to the pseudogap phenomenon, leading to a significant broadening of the single-particle spectral functions. Quantitatively, the broadening of the spectral weights at the BCS gap is characterized by the ratio of the superconducting coherence length and… |
|
Speaker: Federico BonettiTitle: Non-Invertible Symmetries from Holography and BranesVenue: virtualQuantum Matter Seminar Speaker: Federico Bonetti (Oxford) Title: Non-Invertible Symmetries from Holography and Branes Abstract: The notion of global symmetry in quantum field theory (QFT) has witnessed dramatic generalizations in the past few years. One of the most exciting developments has been the identification of 4d QFTs possessing non-invertible symmetries, i.e. global symmetries whose generators exhibit fusion rules that are not group-like. In this talk, I will discuss realizations of non-invertible symmetries in string theory and holography. As a concrete case study, I will consider the Klebanov-Strassler setup for holographic confinement in Type IIB string theory. The global symmetries of the holographic 4d QFT (both invertible and non-invertible) can be accessed by studying the topological couplings of the… |
|
Speaker: Sungwoo HongTitle: Neutrino Masses from Generalized Symmetry BreakingVenue: virtualQuantum Matter Seminar Speaker: Sungwoo Hong (U Chicago & KAIST) Title: Neutrino Masses from Generalized Symmetry Breaking Abstract: We explore generalized global symmetries in theories of physics beyond the Standard Model. Theories of Z′ bosons generically contain ‘non-invertible’ chiral symmetries, whose presence indicates a natural paradigm to break this symmetry by an exponentially small amount in an ultraviolet completion. For example, in models of gauged lepton family difference such as the phenomenologically well-motivated U(1)Lμ−Lτ, there is a non-invertible lepton number symmetry which protects neutrino masses. We embed these theories in gauged non-Abelian horizontal lepton symmetries, e.g. U(1)Lμ−Lτ⊂SU(3)H, where the generalized symmetries are broken nonperturbatively by the existence of lepton family magnetic monopoles. In such theories, either Majorana or… |
|
Speaker: Junkai DongTitle: Exact Many-Body Ground States from Decomposition of Ideal Higher Chern Bands: Applications to Chirally Twisted Graphene MultilayersVenue: virtualQuantum Matter Seminar Speaker: Junkai Dong (Harvard University) Title: Exact Many-Body Ground States from Decomposition of Ideal Higher Chern Bands: Applications to Chirally Twisted Graphene Multilayers Abstract: Motivated by the higher Chern bands of twisted graphene multilayers, we consider flat bands with arbitrary Chern number C with ideal quantum geometry. While C>1 bands differ from Landau levels, we show that these bands host exact fractional Chern insulator (FCI) ground states for short range interactions. We show how to decompose ideal higher Chern bands into separate ideal bands with Chern number 1 that are intertwined through translation and rotation symmetry. The decomposed bands admit an SU(C) action that combines real space and momentum space translations. Remarkably, they also allow… |
|
Speaker: Gabriel WongTitle: 3D gravity and gravitational entanglement entropyVenue: virtualQuantum Matter Seminar Speaker: Gabriel Wong (Harvard CMSA) Title: 3D gravity and gravitational entanglement entropy Abstract: Recent progress in AdS/CFT has provided a good understanding of how the bulk spacetime is encoded in the entanglement structure of the boundary CFT. However, little is known about how spacetime emerges directly from the bulk quantum theory. We address this question in an effective 3d quantum theory of pure gravity, which describes the high temperature regime of a holographic CFT. This theory can be viewed as a $q$-deformation and dimensional uplift of JT gravity. Using this model, we show that the Bekenstein-Hawking entropy of a two-sided black hole equals the bulk entanglement entropy of gravitational edge modes. These edge modes transform… |
|
Speaker: Pok Man TamTitle: Topology of the Fermi sea: Ordinary metals as topological materialsVenue: VirtualQuantum Matter Seminar Speaker: Pok Man Tam (University of Pennsylvania) Title: Topology of the Fermi sea: Ordinary metals as topological materials Abstract: It has long been known that the quantum ground state of a metal is characterized by an abstract manifold in momentum space called the Fermi sea. Fermi sea can be distinguished topologically in much the same way that a ball can be distinguished from a donut by counting the number of holes. The associated topological invariant, i.e. the Euler characteristic (χ_F), serves to classify metals. Here I will survey two recent proposals relating χ_F to experimental observables, namely: (i) equal-time density/number correlations [1], and (ii) Andreev state transport along a planar Josephson junction [2]. Moreover, from the perspective… |
|
Speaker: Daniel S. FreedTitle: Topological symmetry in field theoryVenue: virtualQuantum Matter Seminar Speaker: Daniel S. Freed (U Texas) Title: Topological symmetry in field theory Abstract: Recently there has been lots of activity surrounding generalized notions of symmetry in quantum field theory, including “categorical symmetries,” “higher symmetries,” “noninvertible symmetries,” etc. Inspired by definitions of abstract (finite) groups and algebras and their linear actions, we introduce a framework for these symmetries in field theory and a calculus of topological defects based on techniques in topological field theory. This is joint work with Constantin Teleman and Greg Moore. https://www.youtube.com/watch?v=y5uHfqVGunA&list=PL0NRmB0fnLJQAnYwkpt9PN2PBKx4rvdup&index=26 |
|
Speaker: Francisco MachadoTitle: Kardar-Parisi-Zhang dynamics in integrable quantum magnetsVenue: virtualQuantum Matter Seminar Speaker: Francisco Machado (Berkeley/Harvard) Title: Kardar-Parisi-Zhang dynamics in integrable quantum magnets Abstract: Although the equations of motion that govern quantum mechanics are well-known, understanding the emergent macroscopic behavior that arises from a particular set of microscopic interactions remains remarkably challenging. One particularly important behavior is that of hydrodynamical transport; when a quantum system has a conserved quantity (i.e. total spin), the late-time, coarse-grained dynamics of the conserved charge is expected to follow a simple, classical hydrodynamical description. However the nature and properties of this hydrodynamical description can depend on many details of the underlying interactions. For example, the presence of additional dynamical constraints can fundamentally alter the propagation of the conserved quantity and induce slower-than-diffusion propagation. At the… |