BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//CMSA - ECPv6.15.17//NONSGML v1.0//EN
CALSCALE:GREGORIAN
METHOD:PUBLISH
X-WR-CALNAME:CMSA
X-ORIGINAL-URL:https://cmsa.fas.harvard.edu
X-WR-CALDESC:Events for CMSA
REFRESH-INTERVAL;VALUE=DURATION:PT1H
X-Robots-Tag:noindex
X-PUBLISHED-TTL:PT1H
BEGIN:VTIMEZONE
TZID:America/New_York
BEGIN:DAYLIGHT
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
TZNAME:EDT
DTSTART:20210314T070000
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
TZNAME:EST
DTSTART:20211107T060000
END:STANDARD
BEGIN:DAYLIGHT
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
TZNAME:EDT
DTSTART:20220313T070000
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
TZNAME:EST
DTSTART:20221106T060000
END:STANDARD
BEGIN:DAYLIGHT
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
TZNAME:EDT
DTSTART:20230312T070000
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
TZNAME:EST
DTSTART:20231105T060000
END:STANDARD
BEGIN:DAYLIGHT
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
TZNAME:EDT
DTSTART:20240310T070000
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
TZNAME:EST
DTSTART:20241103T060000
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20231107T163000
DTEND;TZID=America/New_York:20231107T180000
DTSTAMP:20260404T223837
CREATED:20240222T091622Z
LAST-MODIFIED:20240222T091622Z
UID:10002794-1699374600-1699380000@cmsa.fas.harvard.edu
SUMMARY: A Long Exact Sequence in Symmetry Breaking
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Cameron Krulewski (MIT) and Leon Liu (Harvard) \nTitle: A Long Exact Sequence in Symmetry Breaking \nAbstract: We study defects in symmetry breaking phases\, such as domain walls\, vortices\, and hedgehogs. In particular\, we focus on the localized gapless excitations that sometimes occur at the cores of these objects. These are topologically protected by an ’t Hooft anomaly. We classify different symmetry breaking phases in terms of the anomalies of these defects and relate them to the anomaly of the broken symmetry by an anomaly-matching formula. We also derive the obstruction to the existence of a symmetry breaking phase with a local defect. We obtain these results using a long exact sequence of groups of invertible field theories\, which we call the “symmetry breaking long exact sequence” (SBLES). \nThe mathematical backbone of the SBLES is the Smith homomorphism\, which gives a family of maps between twisted bordism groups. Though many examples have been studied\, we give the first completely general account of the Smith homomorphism. We lift it to a map of Thom \nspectra and identify the cofiber\, producing a long exact sequence of twisted bordism groups; the SBLES is the Anderson dual of that long exact sequence. Our work develops further the theory of higher Berry phase and its bulk-boundary correspondence and serves as a new computational tool for classifying symmetry protected topological phases.
URL:https://cmsa.fas.harvard.edu/event/qm_11723/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-11.07.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20231011T163000
DTEND;TZID=America/New_York:20231011T180000
DTSTAMP:20260404T223837
CREATED:20240222T060902Z
LAST-MODIFIED:20240222T060902Z
UID:10002785-1697041800-1697047200@cmsa.fas.harvard.edu
SUMMARY:Non-invertible symmetries\, leptons\, quarks\, and why multiple generations
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Seth Koren (Notre Dame) \nTitle: Non-invertible symmetries\, leptons\, quarks\, and why multiple generations \nAbstract: Generalized global symmetries are present in theories of particle physics\, and understanding their structure can give insight into these theories and UV completions thereof.  After discussing the generalized symmetries of the Standard Model\, we will go Beyond and show that the identification of a non-invertible symmetry of Z’ models of L_µ – L_τ reveals the existence of non-Abelian horizontal gauge theories which naturally produce exponentially small Dirac neutrino masses. Next we will uncover a subtler non-invertible symmetry in horizontal gauge theories of the quark sector which will lead us to a massless down-type quarks solution to strong CP in color-flavor unification. Intriguingly\, this theory works by virtue of the SM having the same numbers of colors and generations.
URL:https://cmsa.fas.harvard.edu/event/qm_101123/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-10.11.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230928T163000
DTEND;TZID=America/New_York:20230928T180000
DTSTAMP:20260404T223837
CREATED:20240221T112307Z
LAST-MODIFIED:20240813T161833Z
UID:10002780-1695918600-1695924000@cmsa.fas.harvard.edu
SUMMARY:Quantum field theory approach to quantum information
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Cenke Xu (UCSB) \nTitle: Quantum field theory approach to quantum information \nAbstract: We apply the formalism of quantum field theory and Euclidean space-time path integral to investigate a class of quantum information problems. In particular\, we investigate quantum many-body systems under weak-measurement and decoherence. The Euclidean space-time path integral allows us to map this problem to a quantum field theory with (temporal) boundary or defects. We therefore investigate two types of quantum many-body systems with nontrivial boundary physics: quantum critical points\, and states with nontrivial topology\, such as Chern insulator and symmetry protected topological states. For example\, we demonstrate that a Wilson-Fisher quantum critical point can be driven into an “extraordinary-log” phase after weak-measurement. Another example is that\, we argue that a system with higher form symmetry may be driven to a self-dual phase transition under weak measurement.
URL:https://cmsa.fas.harvard.edu/event/qm_92823/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-09.28.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230922T100000
DTEND;TZID=America/New_York:20230922T113000
DTSTAMP:20260404T223837
CREATED:20240223T095601Z
LAST-MODIFIED:20240223T095601Z
UID:10002845-1695376800-1695382200@cmsa.fas.harvard.edu
SUMMARY:Floquet codes\, automorphisms\, and quantum computation
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Margarita Davydova (MIT) \nTitle: Floquet codes\, automorphisms\, and quantum computation \nAbstract: In this talk\, I will introduce a new kind of measurement-based quantum computation inspired by Floquet codes. In this model\, the quantum logical gates are implemented by short sequences of low-weight measurements which simultaneously encode logical information and enable error correction.  We introduce a new class of quantum error-correcting codes generalizing Floquet codes that achieve this\, which we call dynamic automorphism (DA) codes. \nAs in Floquet codes\, the instantaneous codespace of a DA code at any fixed point in time is that of a topological code. In this case\, the quantum computation can be viewed as a sequence of time-like domain walls implementing automorphisms of the topological order\, which can be understood in terms of reversible anyon condensation paths in a particular parent model.  This talk will introduce all of these concepts as well as provide a new perspective for thinking about Floquet codes. \nThe explicit examples that we construct\, which we call DA color codes\, can implement the full Clifford group of logical gates in 2+1d by two- and\, rarely three-body measurements. Using adaptive two-body measurements\, we can achieve a non-Clifford gate in 3+1d\, making the first step towards universal quantum computation in this model. \nThe talk is based on recent work with Nathanan Tantivasadakarn\, Shankar Balasubramanian\, and David Aasen [arxiv: 2307.10353].
URL:https://cmsa.fas.harvard.edu/event/qm_92223/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-09.22.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230913T163000
DTEND;TZID=America/New_York:20230913T180000
DTSTAMP:20260404T223837
CREATED:20240223T111403Z
LAST-MODIFIED:20240223T111403Z
UID:10002859-1694622600-1694628000@cmsa.fas.harvard.edu
SUMMARY:Anomalies of Non-Invertible Symmetries
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Clay Córdova (U Chicago) \nTitle: Anomalies of Non-Invertible Symmetries
URL:https://cmsa.fas.harvard.edu/event/qm_91323/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-09.13.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230908T100000
DTEND;TZID=America/New_York:20230908T113000
DTSTAMP:20260404T223837
CREATED:20230904T055802Z
LAST-MODIFIED:20240116T070515Z
UID:10001125-1694167200-1694172600@cmsa.fas.harvard.edu
SUMMARY:A 6-year journey: from gravitational anomaly to a unified theory of generalized symmetry
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Xiao-Gang Wen (MIT) \nTitle: A 6-year journey: from gravitational anomaly to a unified theory of generalized symmetry \nAbstract: Emergent symmetry can be generalized symmetry beyond (higher) group description and/or can be anomalous. I will describe a unified theory for generalized symmetry based on symmetry/topological-order correspondence. I will also discuss some applications of emergent generalized symmetry.
URL:https://cmsa.fas.harvard.edu/event/qm_9823/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-09.08.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230824T100000
DTEND;TZID=America/New_York:20230824T113000
DTSTAMP:20260404T223837
CREATED:20230904T055455Z
LAST-MODIFIED:20240227T085359Z
UID:10001126-1692871200-1692876600@cmsa.fas.harvard.edu
SUMMARY:Two of my favorite numbers: 8 and 24
DESCRIPTION:Quantum Matter Seminar \nSpeaker: John Baez (University of California\, Riverside) \nTitle: Two of my favorite numbers: 8 and 24 \nAbstract: The numbers 8 and 24 play special roles in mathematics. The number 8 is special because of Bott periodicity\, the octonions and the E8 lattice\, while 24 is special for many reasons\, including the binary tetrahedral group\, the 3rd stable homotopy group of spheres\, and the Leech lattice. The number 8 does for superstring theory what the number 24 does for bosonic string theory. In this talk\, which is intended to be entertaining\, I will overview these matters and also some connections between the numbers 8 and 24.
URL:https://cmsa.fas.harvard.edu/event/qm_82423/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-08.24.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230630T100000
DTEND;TZID=America/New_York:20230630T113000
DTSTAMP:20260404T223837
CREATED:20230802T171855Z
LAST-MODIFIED:20240110T074010Z
UID:10001183-1688119200-1688124600@cmsa.fas.harvard.edu
SUMMARY:Monopoles\, Scattering\, and Generalized Symmetries
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Marieke Van Beest (SCGP) \nTitle: Monopoles\, Scattering\, and Generalized Symmetries \nAbstract: In this talk\, we will discuss the problem of electrically charged\, massless fermions scattering off magnetic monopoles. The interpretation of the outgoing states has long been a puzzle\, as they can carry fractional quantum numbers. We argue that such outgoing particles live in the twisted sector of a topological co-dimension 1 surface\, which ends topologically on the monopole. This symmetry defect is often non-invertible\, and as such the outgoing radiation not only carries unconventional flavor quantum numbers\, but is often trailed by a topological field theory\, which is a new prediction.
URL:https://cmsa.fas.harvard.edu/event/qm_63023/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-06.30.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230626T100000
DTEND;TZID=America/New_York:20230626T113000
DTSTAMP:20260404T223837
CREATED:20230802T171648Z
LAST-MODIFIED:20240110T073717Z
UID:10001182-1687773600-1687779000@cmsa.fas.harvard.edu
SUMMARY:Chiral fermionic CFTs of central charge ≤ 16
DESCRIPTION:Quantum Matter Seminar \nTitle: Chiral fermionic CFTs of central charge ≤ 16 \nAbstract: We classified all chiral fermionic CFTs of central charge ≤ 16 using Kac’s theorem and bosonization/fermionization. This talk will discuss the derivation of this result\, its application to the classification of non-supersymmetric heterotic string theories\, and along the way we’ll address some oft-overlooked subtleties of bosonization from the point of view of anomalies and topological phases.
URL:https://cmsa.fas.harvard.edu/event/qm_62623/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-06.26.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230613T100000
DTEND;TZID=America/New_York:20230613T120000
DTSTAMP:20260404T223837
CREATED:20230802T171505Z
LAST-MODIFIED:20240228T070233Z
UID:10001181-1686650400-1686657600@cmsa.fas.harvard.edu
SUMMARY:Small Bosonic CFTs\, Chiral Fermionization\, and Symmetry/Subalgebra Duality
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Brandon C. Rayhaun (C. N. Yang ITP\, Stony Brook University) \nTitle: Small Bosonic CFTs\, Chiral Fermionization\, and Symmetry/Subalgebra Duality \nAbstract: Conformal field theories in (1+1)D are key actors in many dramas of physics and mathematics. Their classification has therefore been an important and long-standing problem. In this talk\, I will explain the main ideas behind the classification of (most) “small” bosonic CFTs. Here\, I use the adjective “small” informally to refer to theories with low central charge (less than 24) and few primary operators (less than 5). Time and attention permitting\, I will highlight two applications of this result. First\, I will describe how it can be used in tandem with bosonization and fermionization techniques to establish the classification of chiral fermionic CFTs with central charge less than 23. Second\, I will showcase how it can be used to bootstrap generalized global symmetries using the concept of “symmetry/subalgebra duality.” \nTalk based on arXiv:2208.05486 [hep-th] (joint work with Sunil Mukhi) and arXiv:2303.16921 [hep-th]. \n \n 
URL:https://cmsa.fas.harvard.edu/event/qm_61323/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-06.13.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230609T100000
DTEND;TZID=America/New_York:20230609T113000
DTSTAMP:20260404T223837
CREATED:20230802T171314Z
LAST-MODIFIED:20240215T111159Z
UID:10001180-1686304800-1686310200@cmsa.fas.harvard.edu
SUMMARY:Classification of Self-Dual Vertex Operator Superalgebras of Central Charge at Most 24
DESCRIPTION:Quantum Matter Seminar \nSpeakers: Gerald Höhn (Kansas State University) & Sven Möller (University of Hamburg) \nTitle: Classification of Self-Dual Vertex Operator Superalgebras of Central Charge at Most 24 \nAbstract: We discuss the classfication of self-dual vertex operator superalgebras (SVOAs) of central charge 24\, or in physics parlance the purely chiral 2-dimensional fermionic conformal field theories with just one primary field. \nThere are exactly 969 such SVOAs under suitable regularity assumptions and the assumption that the shorter moonshine module VB^# is the unique self-dual SVOA of central charge 23.5 whose weight-1/2 and weight-1 spaces vanish. \nWe construct and classify the self-dual SVOAs by determining the 2-neighbourhood graph of the self-dual (purely bosonic) VOAs of central charge 24 and also by realising them as simple-current extensions of a dual pair containing a certain maximal lattice VOA. We show that all SVOAs besides VB^# x F and potential fake copies thereof stem from elements of the Conway group Co_0\, the automorphism group of the Leech lattice. \nBy splitting off free fermions F\, if possible\, we obtain the classification for all central charges less than or equal to 24.\nReference: G. Höhn\, S. Möller\, arXiv:2303.17190.
URL:https://cmsa.fas.harvard.edu/event/qm_6923/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-06.09.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230512T100000
DTEND;TZID=America/New_York:20230512T113000
DTSTAMP:20260404T223837
CREATED:20230802T171128Z
LAST-MODIFIED:20240215T111609Z
UID:10001179-1683885600-1683891000@cmsa.fas.harvard.edu
SUMMARY:Anomalies of (1+1)D categorical symmetries
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Carolyn Zhang (U Chicago) \nTitle: Anomalies of (1+1)D categorical symmetries \nAbstract: 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 different gapped boundary\, given by a \emph{magnetic} Lagrangian algebra\, then there exists a gapped phase where $A$ is not spontaneously broken at all\, which means that $A$ is not anomalous. In certain cases\, we show that requiring the existence of such a magnetic Lagrangian algebra leads to highly computable obstructions to $A$ being anomaly-free. As an application\, we consider the Drinfeld centers of $\mathbb{Z}_N\times\mathbb{Z}_N$ Tambara-Yamagami fusion categories and recover known results from the study of fiber functors.
URL:https://cmsa.fas.harvard.edu/event/qm_51223/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-05.12.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230505T100000
DTEND;TZID=America/New_York:20230505T113000
DTSTAMP:20260404T223837
CREATED:20230802T170945Z
LAST-MODIFIED:20240110T072755Z
UID:10001178-1683280800-1683286200@cmsa.fas.harvard.edu
SUMMARY:Detecting central charge in a superconducting quantum processor
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Sona Najafi (IBM Quantum) \nTitle: Detecting central charge in a superconducting quantum processor \nAbstract: 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 Shannon-Renyi entropy on a local basis of a one-dimensional 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 open and periodic boundary conditions and perform local Pauli X and Z basis measurements. Using error mitigation such as probabilistic error cancellation\, we extract an estimation of the local Pauli observables needed to determine the Shannon-Renyi entropy with respect to subsystem size. Finally\, we obtain the central charge in the sub-leading term of Shannon-Renyi entropy.
URL:https://cmsa.fas.harvard.edu/event/qm_5523/
LOCATION:Hybrid – G10
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-05.05.23-2.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230428T100000
DTEND;TZID=America/New_York:20230428T113000
DTSTAMP:20260404T223837
CREATED:20230802T170750Z
LAST-MODIFIED:20240215T115157Z
UID:10001177-1682676000-1682681400@cmsa.fas.harvard.edu
SUMMARY:Fracton Self-Statistics
DESCRIPTION:Quantum Matter Seminar \nTitle: Fracton Self-Statistics \nSpeaker: Hao Song (ITP-CAS) \nAbstract: 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 self-exchange statistics be naturally defined for fractons\, given their complete immobility as isolated excitations? Surprisingly\, we demonstrate how fractons can be exchanged\, and show their self-statistics is a key part of the characterization of fracton orders. We derive general constraints satisfied by the fracton self-statistics in a large class of abelian fracton orders. Finally\, we show the existence of semionic or fermionic fracton self-statistics in some twisted variants of the checkerboard model and Haah’s code\, establishing that these models are in distinct quantum phases as compared to their untwisted cousins. \nReferences: H Song\, N Tantivasadakarn\, W Shirley\, M Hermele\, arXiv:2304.00028.
URL:https://cmsa.fas.harvard.edu/event/qm_42823/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-04.28.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230421T100000
DTEND;TZID=America/New_York:20230421T113000
DTSTAMP:20260404T223837
CREATED:20230802T170556Z
LAST-MODIFIED:20240131T001826Z
UID:10001176-1682071200-1682076600@cmsa.fas.harvard.edu
SUMMARY:A model of the cuprates: from the pseudogap metal to d-wave superconductivity and charge order
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Prof. Subir Sachdev (Harvard) \nTitle: A model of the cuprates: from the pseudogap metal to d-wave superconductivity and charge order \nAbstract: Soon after the discovery of high-temperature superconductivity in the cuprates\, Anderson proposed a connection to quantum spin liquids. But observations since then have shown that the low-temperature phase diagram is dominated by conventional states\, with a competition between superconductivity and charge-ordered 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 single-band model\, with small pocket Fermi surfaces of electron-like quasiparticles whose enclosed area is not equal to the free electron value\, and an underlying pi-flux spin liquid with an emergent SU(2) gauge field. This pi-flux spin liquid is now known to be unstable to confinement at sufficiently low energies. We develop a theory of the different routes to confinement of the pi-flux spin liquid and show that d-wave superconductivity\, antiferromagnetism\, and charge order are natural outcomes. We argue that this theory provides routes to resolving a number of open puzzles on the cuprate phase diagram.\nAs a side result\, at half-filling\, we propose a deconfined quantum critical point between an antiferromagnet and a d-wave superconductor described by a conformal gauge theory of 2 flavors of massless Dirac fermions and 2 flavors of complex scalars coupled as fundamentals to a SU(2) gauge field.\nThis talk is based on Maine Christos\, Zhu-Xi Luo\, Henry Shackleton\, Mathias S. Scheurer\, and S. S.\, arXiv:2302.07885
URL:https://cmsa.fas.harvard.edu/event/qm_42123/
LOCATION:Hybrid – G10
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-04.21.23-1.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230414T100000
DTEND;TZID=America/New_York:20230414T113000
DTSTAMP:20260404T223837
CREATED:20230802T170408Z
LAST-MODIFIED:20240110T072019Z
UID:10001175-1681466400-1681471800@cmsa.fas.harvard.edu
SUMMARY:Fault-tolerant quantum computation via topological order on fractals and emergent symmetries
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Guanyu Zhu (IBM Quantum\, T. J. Watson Research Center) \nTitle: Fault-tolerant quantum computation via topological order on fractals and emergent symmetries \nAbstract: 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 fault-tolerant non-Clifford logical gates in such fractal codes using the idea of emergent symmetries. In particular\, I will discuss the existence of higher-form symmetries corresponding to sweeping of certain codimension-2 invertible defects and exotic gapped boundaries which condense such defects. \nReferences:\n1. PRX Quantum 3 (3)\, 030338 (2022)\, Guanyu Zhu\, Tomas Jochym-O’Connor\, Arpit Dua\n2. arXiv:2201.03568 (2022)\, Arpit Dua\, Tomas Jochym-O'Connor\, Guanyu Zhu\n3. arXiv:2208.07367 (2022)\, Maissam Barkeshli\, Yu-An Chen\, Sheng-Jie Huang\, Ryohei Kobayashi\, Nathanan Tantivasadakarn\, Guanyu Zhu \n 
URL:https://cmsa.fas.harvard.edu/event/qm_4142023/
LOCATION:Hybrid – G10
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-04.14.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230407T100000
DTEND;TZID=America/New_York:20230407T113000
DTSTAMP:20260404T223837
CREATED:20230802T170222Z
LAST-MODIFIED:20240110T071718Z
UID:10001174-1680861600-1680867000@cmsa.fas.harvard.edu
SUMMARY:Enhancing Detection of Topological Order by Local Error Correction
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Nishad Maskara (Harvard) \nTitle: Enhancing Detection of Topological Order by Local Error Correction \nAbstract: 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 applicable in the presence of incoherent noise sources\, making it particularly suitable for realistic experiments. We demonstrate the power of LED using numerical simulations of the toric code under a variety of perturbations\, and we subsequently apply it to an experimental realization of a quantum spin liquid using a Rydberg-atom quantum simulator.  Finally\, we illustrate how LED can be applied to more general phases including non-abelian topological orders. \n 
URL:https://cmsa.fas.harvard.edu/event/qm_4723/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-04.07.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230324T100000
DTEND;TZID=America/New_York:20230324T113000
DTSTAMP:20260404T223837
CREATED:20230802T165633Z
LAST-MODIFIED:20240110T055248Z
UID:10001172-1679652000-1679657400@cmsa.fas.harvard.edu
SUMMARY:Traversable wormhole dynamics on a quantum processor
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Alexander Zlokapa\, MIT \nTitle: Traversable wormhole dynamics on a quantum processor \nAbstract: 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 be used to probe the SYK traversable wormhole dynamics through the corresponding teleportation protocol. This can be realized as a quantum circuit\, equivalent to the gravitational picture in the semiclassical limit of an infinite number of qubits. Here we use learning techniques to construct a sparsified SYK model that we experimentally realize with 164 two-qubit gates on a nine-qubit circuit and observe the corresponding traversable wormhole dynamics. Despite its approximate nature\, the sparsified SYK model preserves key properties of the traversable wormhole physics: perfect size winding\, coupling on either side of the wormhole that is consistent with a negative energy shockwave\, a Shapiro time delay\, causal time-order of signals emerging from the wormhole\, and scrambling and thermalization dynamics. Our experiment was run on the Google Sycamore processor. By interrogating a two-dimensional gravity dual system\, our work represents a step towards a program for studying quantum gravity in the laboratory. Future developments will require improved hardware scalability and performance as well as theoretical developments including higher-dimensional quantum gravity duals and other SYK-like models. \n 
URL:https://cmsa.fas.harvard.edu/event/qm_32423/
LOCATION:Hybrid – G10
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-03.24.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230317T100000
DTEND;TZID=America/New_York:20230317T113000
DTSTAMP:20260404T223837
CREATED:20230802T165348Z
LAST-MODIFIED:20240228T091308Z
UID:10001171-1679047200-1679052600@cmsa.fas.harvard.edu
SUMMARY:Tensorial TQFT and disentangling modular Walker-Wang models
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Andreas Bauer  (Freie Universität Berlin) \nTitle: Tensorial TQFT and disentangling modular Walker-Wang models \nAbstract: 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. \n 
URL:https://cmsa.fas.harvard.edu/event/qm_31723/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Quantum Matter
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230310T100000
DTEND;TZID=America/New_York:20230310T110000
DTSTAMP:20260404T223837
CREATED:20230802T165201Z
LAST-MODIFIED:20240110T054801Z
UID:10001170-1678442400-1678446000@cmsa.fas.harvard.edu
SUMMARY:Quantum entropy thermalization
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Yichen Huang (Harvard) \nTitle: Quantum entropy thermalization \nAbstract: 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. \nReferences: arXiv:2302.10165\, 2209.09826; Joint work with Aram W. Harrow \n 
URL:https://cmsa.fas.harvard.edu/event/qm_31023/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-03.10.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230303T100000
DTEND;TZID=America/New_York:20230303T113000
DTSTAMP:20260404T223837
CREATED:20230802T164922Z
LAST-MODIFIED:20240819T145549Z
UID:10001169-1677837600-1677843000@cmsa.fas.harvard.edu
SUMMARY:Strongly coupled ultraviolet fixed point and symmetric mass generation in four dimensions with 8 Kähler-Dirac fermions
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Anna Hasenfratz (University of Colorado) \nTitle: Strongly coupled ultraviolet fixed point and symmetric mass generation in four dimensions with 8 Kähler-Dirac fermions\n\nAbstract: 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.\n\nLattice 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 14 for fundamental fermions.\n\nUsing an improved lattice actions that include heavy Pauli-Villars (PV) type bosons to reduce ultraviolet fluctuations\, I was able to simulate an SU(3) system with 8 fundamental flavors at much stronger renormalized coupling than previously possibly. The numerical results indicate a smooth phase transition from weak coupling to a strongly coupled phase.\nI investigate the critical behavior of the transition using finite size scaling. The result of the scaling analysis is not consistent with a first order phase transition\, but it is well described by   Berezinsky-Kosterlitz-Thouless or BKT scaling. BKT scaling could imply that the 8-flavor system is the opening of the conformal window\, an exciting possibility that warrants further investigations.\n\nThe strongly coupled phase appear to be chirally symmetric but gapped\, suggesting symmetric mass generation (SMG). This could be the consequence of the lattice fermions used in this study. Staggered fermions in the massless limit are known to be anomaly free\, allowing an SMG phase in the continuum limit.\n  \n\n\nReferences:\nPhys.Rev.D 106 (2022) 1\, 014513 • e-Print: 2204.04801\nPhys.Rev.D 104 (2021) 7\, 074509 • e-Print: 2109.02790\nFor anomalies and staggered fermion\, see\nPhys.Rev.D 104 (2021) 9\, 094504 • e-Print: 2101.01026\n\nhttps://www.youtube.com/watch?v=3jtNsFGszjE&list=PL0NRmB0fnLJQAnYwkpt9PN2PBKx4rvdup&index=14
URL:https://cmsa.fas.harvard.edu/event/qm_3323/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-03.03.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230217T100000
DTEND;TZID=America/New_York:20230217T113000
DTSTAMP:20260404T223837
CREATED:20230802T164725Z
LAST-MODIFIED:20240813T161921Z
UID:10001168-1676628000-1676633400@cmsa.fas.harvard.edu
SUMMARY:Quantum Spin Lakes: NISQ-Era Spin Liquids from Non-Equilibrium Dynamics
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Rahul Sahay (Harvard) \nTitle: Quantum Spin Lakes: NISQ-Era Spin Liquids from Non-Equilibrium Dynamics \nAbstract: 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 recent experimental and numerical observations of the dynamical state preparation of the ruby lattice spin liquid in Rydberg atom arrays. Time permitting\, we will discuss how our theory motivates a tree tensor network-based numerical tool—reliant on our theory—that quantitatively reproduces the experimental data two orders of magnitude faster than conventional brute-force simulation methods. Finally\, we will highlight that even spin liquid states that are unstable in equilibrium—namely\, 2 + 1D U(1) spin liquid states—can be robustly prepared by non-equilibrium dynamics. \n 
URL:https://cmsa.fas.harvard.edu/event/qm_21723/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-02.17.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230210T103000
DTEND;TZID=America/New_York:20230210T113000
DTSTAMP:20260404T223837
CREATED:20230802T164450Z
LAST-MODIFIED:20240216T083704Z
UID:10001167-1676025000-1676028600@cmsa.fas.harvard.edu
SUMMARY:Non-invertible Symmetry Enforced Gaplessness
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Ho Tat Lam (MIT) \nTitle: Non-invertible Symmetry Enforced Gaplessness \nAbstract: 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. \n 
URL:https://cmsa.fas.harvard.edu/event/qm_21023/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-02.10.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230203T103000
DTEND;TZID=America/New_York:20230203T113000
DTSTAMP:20260404T223837
CREATED:20230802T164259Z
LAST-MODIFIED:20240215T100905Z
UID:10001166-1675420200-1675423800@cmsa.fas.harvard.edu
SUMMARY:Fracton orders in hyperbolic space and its excitations with fractal mobility
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Han Yan (Rice U) \nTitle: Fracton orders in hyperbolic space and its excitations with fractal mobility \nAbstract: 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 by a membrane operator (as in the X-cube model) or by a fractal-shaped operator within the hyperbolic plane. Our work shows that there are still plenty of exotic behaviors from fracton order to be explored\, especially when the embedding geometry is curved. \nReference: H. Yan\, K. Slage\, A. H. Nevidomskyy\, arXiv:2211.15829 \n 
URL:https://cmsa.fas.harvard.edu/event/qm_2323/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-02.03.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230130T093000
DTEND;TZID=America/New_York:20230130T103000
DTSTAMP:20260404T223837
CREATED:20230802T163915Z
LAST-MODIFIED:20240215T101107Z
UID:10001165-1675071000-1675074600@cmsa.fas.harvard.edu
SUMMARY:Group Invariant States as Many-Body Scars
DESCRIPTION:Quantum Matter Seminar \nTitle: Group Invariant States as Many-Body Scars \nSpeaker: Igor R. Klebanov (Princeton University) \nAbstract: 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 systems where group singlet states have special properties: the matrix quantum mechanics and fermionic tensor models. We continue on to appropriately deformed versions of the SU(2) Hubbard model and show that the scar subsector is invariant under a large group\, which acts on the lattice sites. More generally\, we apply this idea to lattice systems with N sites that contain M Majorana fermions per site. The Hilbert space may be decomposed under the action of the SO(N)xSO(M) group\, and the scars are the SO(N) singlets. For any even M\, there are two families of scars. One of them\, which we call the eta-states\, is symmetric under the group O(N) that includes a reflection. The other\, the zeta-states\, has the SO(N) invariance only. For M=4\, where our construction reduces to a deformed SU(2) Hubbard chain with local interactions\, the former family are the N+1 eta-pairing states\, while the latter are the N+1 states of maximum spin. For M=6\, we exhibit explicit formulae for the scar states and calculate the bipartite entanglement entropy analytically. For large N\, it grows logarithmically with the region size. In general\, the energies of the scars within each family are not equidistant. For M>6 we also find that\, with local Hamiltonians\, the scars typically have certain degeneracies.  The latter part of the talk is based on the recent paper “Majorana Scars as Group Singlets” by Zimo Sun\, Fedor Popov\, Igor Klebanov and Kiryl Pakrouski\, arXiv:2212.11914 \n 
URL:https://cmsa.fas.harvard.edu/event/qm_13023/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-1.30.23-1.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230124T131500
DTEND;TZID=America/New_York:20230124T144500
DTSTAMP:20260404T223837
CREATED:20230802T163601Z
LAST-MODIFIED:20240110T053406Z
UID:10001164-1674566100-1674571500@cmsa.fas.harvard.edu
SUMMARY:Reflections on Parity Breaking
DESCRIPTION:Quantum Matter Seminar \nSpeakers: Jacob McNamara (Caltech) and Matthew Reece (Harvard) \nTitle: Reflections on Parity Breaking \nAbstract: 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 quantum gravity\, as well as their relationship with the Swampland Cobordism Conjecture. \n 
URL:https://cmsa.fas.harvard.edu/event/qm_12423/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-1.24.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20221220T090000
DTEND;TZID=America/New_York:20221220T103000
DTSTAMP:20260404T223837
CREATED:20240215T105412Z
LAST-MODIFIED:20240819T150130Z
UID:10002746-1671526800-1671532200@cmsa.fas.harvard.edu
SUMMARY:Phase Fluctuations in Two-Dimensional Superconductors and Pseudogap Phenomenon
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Yang Qi (Fudan) \nTitle: Phase Fluctuations in Two-Dimensional Superconductors and Pseudogap Phenomenon \nAbstract: 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 the spatial correlation length of the superconducting pairing order parameter. Our results are tested on the attractive-U fermion Hubbard model on the square lattice\, using unbiased determinant quantum Monte Carlo method and stochastic analytic continuation. We also apply our method to 2d superconductors with d-wave pairing and observe that the phase fluctuations may lead to Fermi-arc phenomenon above the BKT transition.
URL:https://cmsa.fas.harvard.edu/event/qm_122022/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-Seminar-12.20.22.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20221212T090000
DTEND;TZID=America/New_York:20221212T103000
DTSTAMP:20260404T223837
CREATED:20240215T095743Z
LAST-MODIFIED:20240819T150302Z
UID:10002733-1670835600-1670841000@cmsa.fas.harvard.edu
SUMMARY:Non-Invertible Symmetries from Holography and Branes
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Federico Bonetti (Oxford) \nTitle: Non-Invertible Symmetries from Holography and Branes \nAbstract:  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 low-energy effective action of the dual 5d supergravity theory. Moreover\, non-invertible symmetry defects can be realized in terms of D-branes. The D-brane picture captures non-trivial aspects of the fusion of non-invertible symmetry defects\, and of their action on extended operators of the 4d QFT.
URL:https://cmsa.fas.harvard.edu/event/qm_121222/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-12.12.22.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20221206T090000
DTEND;TZID=America/New_York:20221206T103000
DTSTAMP:20260404T223837
CREATED:20240215T094810Z
LAST-MODIFIED:20240819T150002Z
UID:10002729-1670317200-1670322600@cmsa.fas.harvard.edu
SUMMARY:Neutrino Masses from Generalized Symmetry Breaking
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Sungwoo Hong (U Chicago & KAIST) \nTitle: Neutrino Masses from Generalized Symmetry Breaking \nAbstract: 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 Dirac neutrino masses may be generated through quantum gauge theory effects from the charged lepton Yukawas e.g. yν∼yτexp(−Sinst). These theories require no bevy of new fields nor ad hoc additional global symmetries\, but are instead simple\, natural\, and predictive: the discovery of a lepton family Z′ at low energies will reveal the scale at which Lμ−Lτ emerges from a larger gauge symmetry. \n 
URL:https://cmsa.fas.harvard.edu/event/qm_12622/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-Seminar-12.06.22.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20221205T090000
DTEND;TZID=America/New_York:20221205T103000
DTSTAMP:20260404T223837
CREATED:20240215T100106Z
LAST-MODIFIED:20240819T150452Z
UID:10002734-1670230800-1670236200@cmsa.fas.harvard.edu
SUMMARY:Exact Many-Body Ground States from Decomposition of Ideal Higher Chern Bands: Applications to Chirally Twisted Graphene Multilayers
DESCRIPTION:Quantum Matter Seminar \nSpeaker: Junkai Dong (Harvard University) \nTitle: Exact Many-Body Ground States from Decomposition of Ideal Higher Chern Bands: Applications to Chirally Twisted Graphene Multilayers \nAbstract: 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 for analytic construction of exact many-body ground states\, such as generalized quantum Hall ferromagnets and FCIs\, including flavor-singlet Halperin states and Laughlin ferromagnets in the limit of short-range interactions. In this limit\, the SU(C) action is promoted to a symmetry on the ground state subspace. While flavor singlet states are translation symmetric\, the flavor ferromagnets correspond to translation broken states and admit charged skyrmion excitations corresponding to a spatially varying density wave pattern. We confirm our analytic predictions with numerical simulations of ideal bands of twisted chiral multilayers of graphene\, and discuss consequences for experimentally accessible systems such as monolayer graphene twisted relative to a Bernal bilayer. \n 
URL:https://cmsa.fas.harvard.edu/event/qm_12522/
LOCATION:Virtual
CATEGORIES:Quantum Matter
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-QMMP-Seminar-12.5.22.png
END:VEVENT
END:VCALENDAR