
Speaker: Carolyn ZhangTitle: Anomalies of (1+1)D categorical symmetriesVenue: virtualQuantum Matter Seminar Speaker: Carolyn Zhang (U Chicago) Title: Anomalies of (1+1)D categorical symmetries Abstract: We present a general approach for detecting when a fusion category symmetry is anomalous, based on the existence of a special kind of Lagrangian algebra of the corresponding Drinfeld center. The Drinfeld center of a fusion category $A$ describes a $(2+1)D$ topological order whose gapped boundaries enumerate all $(1+1)D$ gapped phases with the fusion category symmetry, which may be spontaneously broken. There always exists a gapped boundary, given by the \emph{electric} Lagrangian algebra, that describes a phase with $A$ fully spontaneously broken. The symmetry defects of this boundary can be identified with the objects in $A$. We observe that if there exists a… 

Speaker: Sona NajafiTitle: Detecting central charge in a superconducting quantum processorVenue: Hybrid G10Quantum Matter Seminar Speaker: Sona Najafi (IBM Quantum) Title: Detecting central charge in a superconducting quantum processor Abstract: Physical systems at the continuous phase transition point exhibit conformal symmetry rendering local scaling invariance. In two dimensions, the conformal group possesses infinite generators described by Virasoro algebra with an essential parameter known as a central charge. While the central charge manifests itself in a variety of quantities, its detection in experimental setup remains elusive. In this work, we utilize ShannonRenyi entropy on a local basis of a onedimensional quantum spin chain at a critical point. We first use a simulated variational quantum eigen solver to prepare the ground state of the critical transfer field Ising model and XXZ model with… 

Speaker: Hao SongTitle: Fracton SelfStatisticsVenue: virtualQuantum Matter Seminar Title: Fracton SelfStatistics Speaker: Hao Song (ITPCAS) Abstract: Fracton order describes novel quantum phases of matter that host quasiparticles with restricted mobility, and thus lies beyond the existing paradigm of topological order. In particular, excitations that cannot move without creating other excitations are called fractons. Here we address a fundamental open question — can the notion of selfexchange statistics be naturally defined for fractons, given their complete immobility as isolated excitations? Surprisingly, we demonstrate how fractons can be exchanged, and show their selfstatistics is a key part of the characterization of fracton orders. We derive general constraints satisfied by the fracton selfstatistics in a large class of abelian fracton orders. Finally, we show the existence… 

Speaker: Subir SachdevTitle: A model of the cuprates: from the pseudogap metal to dwave superconductivity and charge orderVenue: Hybrid G10Quantum Matter Seminar Speaker: Prof. Subir Sachdev (Harvard) Title: A model of the cuprates: from the pseudogap metal to dwave superconductivity and charge order Abstract: Soon after the discovery of hightemperature superconductivity in the cuprates, Anderson proposed a connection to quantum spin liquids. But observations since then have shown that the lowtemperature phase diagram is dominated by conventional states, with a competition between superconductivity and chargeordered states which break translational symmetry. We employ the “pseudogap metal” phase, found at intermediate temperatures and low hole doping, as the parent to the phases found at lower temperatures. The pseudogap metal is described as a fractionalized phase of a singleband model, with small pocket Fermi surfaces of electronlike quasiparticles whose enclosed… 

Speaker: Guanyu ZhuTitle: Faulttolerant 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: Faulttolerant 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 spacetime overhead for universal faulttolerant 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 topologicallyordered states of matter is a longstanding goal at the interface of several subfields of the physical sciences. Such states feature intriguing physical properties such as longrange entanglement, emergent gauge fields and nonlocal correlations, and can aid in realization of scalable faulttolerant quantum computation. However, these same features also make creation, detection, and characterization of topologicallyordered states particularly challenging. Motivated by recent experimental demonstrations, we introduce a new paradigm for quantifying topological states—locally errorcorrected decoration (LED)—by combining methods of error correction with ideas of renormalizationgroup 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 semiinfinite geometry can exhibit an “extraordinarylog” boundary universality class, where the spinspin correlation function on the boundary falls off as (log x)^(q). This universality class exists for a range 2≤N<Nc and MonteCarlo 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 extraordinarylog 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: virtualQuantum 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 lowerdimensional boundary. The antide 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 manybody 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 WalkerWang modelsVenue: CMSA Room G10Quantum Matter Seminar Speaker: Andreas Bauer (Freie Universität Berlin) Title: Tensorial TQFT and disentangling modular WalkerWang 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 WalkerWang models. 

Speaker: Yichen HuangTitle: Quantum entropy thermalizationVenue: virtualQuantum Matter Seminar Speaker: Yichen Huang (Harvard) Title: Quantum entropy thermalization Abstract: In an isolated quantum manybody 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 SachdevYeKitaev model initialized in a pure product state. The model is obtained by adding random alltoall 4body interactions as a perturbation to a random freefermion 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 KählerDirac 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 KählerDirac fermions Abstract: 4dimensional gaugefermion 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 nonphysical 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: NISQEra Spin Liquids from NonEquilibrium DynamicsVenue: virtualQuantum Matter Seminar Speaker: Rahul Sahay (Harvard) Title: Quantum Spin Lakes: NISQEra Spin Liquids from NonEquilibrium Dynamics Abstract: While manybody 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 nonequilibrium 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 “unHiggs”), yielding a QSLlike state. We christen such states “quantum spin lakes” which, while not thermodynamically large QSLs, enable their study in NISQera quantum simulators. Indeed, we show that this mechanism sheds light on… 

Speaker: Ho Tat LamTitle: Noninvertible Symmetry Enforced GaplessnessVenue: virtualQuantum Matter Seminar Speaker: Ho Tat Lam (MIT) Title: Noninvertible Symmetry Enforced Gaplessness Abstract: Quantum systems in 3+1dimensions that are invariant under gauging a oneform symmetry enjoy novel noninvertible duality symmetries encoded by topological defects. These symmetries are renormalization group invariants which constrain infrared dynamics. We show that such noninvertible symmetries often forbid a symmetrypreserving vacuum state with a gapped spectrum, leaving only two possibilities for the infrared dynamics: a gapless state or spontaneous breaking of the noninvertible symmetries. These noninvertible symmetries are realized in lattice gauge theories, which serve to illustrate our results. 

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 Xcube 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 fractalshaped 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 ManyBody ScarsVenue: virtualQuantum Matter Seminar Title: Group Invariant States as ManyBody Scars Speaker: Igor R. Klebanov (Princeton University) Abstract: Quantum manybody scars have been an active area of research in Condensed Matter Physics for several years. In some manybody 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 manybody… 

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 NelsonBarr 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 TwoDimensional Superconductors and Pseudogap PhenomenonVenue: virtualQuantum Matter Seminar Speaker: Yang Qi (Fudan) Title: Phase Fluctuations in TwoDimensional Superconductors and Pseudogap Phenomenon Abstract: We study the phase fluctuations in the normal state of a general twodimensional (2d) superconducting system with swave 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 BerenzinskiiKosterlitzThouless (BKT) transition give birth to the pseudogap phenomenon, leading to a significant broadening of the singleparticle 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: NonInvertible Symmetries from Holography and BranesVenue: virtualQuantum Matter Seminar Speaker: Federico Bonetti (Oxford) Title: NonInvertible 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 noninvertible symmetries, i.e. global symmetries whose generators exhibit fusion rules that are not grouplike. In this talk, I will discuss realizations of noninvertible symmetries in string theory and holography. As a concrete case study, I will consider the KlebanovStrassler setup for holographic confinement in Type IIB string theory. The global symmetries of the holographic 4d QFT (both invertible and noninvertible) 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 ‘noninvertible’ 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 wellmotivated U(1)Lμ−Lτ, there is a noninvertible lepton number symmetry which protects neutrino masses. We embed these theories in gauged nonAbelian 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 ManyBody 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 ManyBody 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… 