Quantum Matter in Mathematics and Physics 2020-2021

Beginning immediately, until at least December 31, all seminars will take place virtually, through Zoom.

The second Quantum Matter Workshop has been postponed. Accordingly, scheduled talks will be rearranged to take place in this seminar throughout the summer.

To learn how to attend this seminar, please fill out this form. 

Previous Quantum Matter/Condensed Matter Seminar schedule information and video links can be found here.

As part of the program on Quantum Matter in Mathematics and Physics, the CMSA will be hosting two weekly seminars. The Quantum Matter/Quantum Field Theory seminar will take place Wednesdays from 10:30 – 12:00pm on Zoom.  The Condensed Matter/Math Seminar will take place on Thursdays from 10:30 – 12:00pm on Zoom.  In addition to the Quantum Matter seminar, the CMSA will also be hosting a related seminar series on a Strongly Correlated Quantum Materials and High-Temperature Superconductors. Please email the seminar organizer to obtain a link.

The schedules for both seminars will be updated below as speakers are confirmed:

Fall 2020:

Subir Sachdev (Harvard University)

This meeting will be taking place virtually on Zoom.

Title: Metal-to-metal quantum phase transitions not described by symmetry-breaking orders

Abstract: Numerous experiments have explored the phases of the cuprates with increasing doping density p from the antiferromagnetic insulator. There is now strong evidence that the small p region is a novel phase of matter, often called the pseudogap metal, separated from conventional Fermi liquid at larger p by a quantum phase transition. Symmetry-breaking orders play a spectator role, at best, at this quantum phase transition. I will describe trial wavefunctions across this metal-metal transition employing hidden layers of ancilla qubits (proposed by Ya-Hui Zhang). Quantum fluctuations are described by a gauge theory  of ghost fermions that carry neither spin nor charge. I will also
describe a separate approach to this transition in a t-J model with random exchange interactions in the limit of large dimensions. This approach leads to a partly solvable SYK-like critical theory of holons and spinons, and a linear in temperature resistivity from time reparameterization fluctuations. Near criticality, both approaches have in common emergent fractionalized excitations, and a significantly larger entropy than naively expected.
9:30 – 11:00am
Janet Ling Yan Hung (Fudan University)

This meeting will be taking place virtually on Zoom.

TitleGapped Boundaries, Junctions via (fermionic) anyon condensation

Abstract: We study gapped boundaries characterized by “fermionic condensates” in 2+1 d topological order. Mathematically, each of these condensates can be described by a super commutative Frobenius algebra. We systematically obtain the species of excitations at the gapped boundary/ junctions, and study their endomorphisms (ability to trap a Majorana fermion) and fusion rules, and generalized the defect Verlinde formula to a twisted version. We illustrate these results with explicit examples. We will also comment on the connection with topological defects in spin CFTs. We will review necessary mathematical details of Frobenius algebra and their modules that we made heavy use of. 
9/9/2020Ying-Hsuan Lin (Caltech)


This meeting will be taking place virtually on Zoom.

TitleExotic Consistent (1+1)d Anomalies: A Ghost Story

Abstract:  We revisit ‘t Hooft anomalies in (1+1)d non-spin quantum field theory, starting from the consistency and locality conditions, and find that consistent U(1) and gravitational anomalies cannot always be canceled by properly quantized (2+1)d classical Chern-Simons actions.  On the one hand, we prove that certain exotic anomalies can only be realized by non-unitary or non-compact theories; on the other hand, without insisting on unitarity, the exotic anomalies present a small caveat to the inflow paradigm.  For the mixed U(1) gravitational anomaly, we propose an inflow mechanism involving a mixed U(1) x SO(2) classical Chern-Simons action, with a boundary condition that matches the SO(2) gauge field with the (1+1)d spin connection.  Furthermore, we show that this mixed anomaly gives rise to an isotopy anomaly of U(1) topological defect lines.  The holomorphic bc ghost system realizes all the exotic consistent anomalies.
9/10/2020Maissam Barkeshli (Maryland)This meeting will be taking place virtually on Zoom.

Title: Absolute anomalies in (2+1)D symmetry-enriched topological states and exact (3+1)D constructions

Abstract: Certain patterns of symmetry fractionalization in (2+1)D topologically ordered phases of matter can be anomalous, which means that they possess an obstruction to being realized in purely (2+1)D. In this talk, I will explain our recent results showing how to compute the anomaly for symmetry-enriched topological (SET) states of bosons in complete generality. Given any unitary modular tensor category (UMTC) and symmetry fractionalization class for a global symmetry group G, I will show how to define a (3+1)D topologically invariant path integral in terms of a state sum for a G symmetry- protected topological (SPT) state. This also determines an exactly solvable Hamiltonian for the system which possesses a (2+1)D G symmetric surface termination that hosts deconfined anyon excitations described by the given UMTC and symmetry fractionalization class. This approach applies to general symmetry groups, including anyon-permuting and anti-unitary symmetries. In the case of unitary orientation-preserving symmetries, our results can also be viewed as providing a method to compute the H4(G,U(1)) obstruction that arises in the theory of G-crossed braided tensor categories, for which no general method has been presented to date. This is joint work with D. Bulmash, presented in arXiv:2003.11553
9/16/2020Andreas Karch (UT Austin)

This meeting will be taking place virtually on Zoom.

Title: Branes, Black Holes and Islands

Abstract: I’ll review the basic construction of Randall-Sundrum braneworlds and some of their applications to formal problems in quantum field theory. I will highlight some recent results regarding scenarios with mismatched brane tensions. In the last part of the talk, I’ll review how RS branes have led to exciting new results regarding evaporation of black holes and will put emphasis on the interesting role the graviton mass plays in these discussions.
9/17/2020Roger Mong (University of Pittsburgh) Title: Universal multipartite entanglement in quantum spin chains

Abstract: Quantum entanglement has played a key role in studying emergent phenomena in strongly-correlated many-body systems.  Remarkably, The entanglement properties of the ground state encodes information on the nature of excitations.  Here we introduce two new entanglement measures $g(A:B)$ and $h(A:B)$ which characterizes certain tripartite entanglement between $A$, $B$, and the environment.  The measures are based off of the entanglement of purification and the reflected entropy popular among holography.  For 1D states, the two measures are UV insensitive and yield universal quantities for symmetry-broken, symmetry preserved, and critical phases.  We conclude with a few remarks regarding applications to 2D phases.
9/23/2020Subir Sachdev (Harvard University)Title: Metal-to-metal quantum phase transitions not described by symmetry-breaking orders II

Abstract: In this second talk, I will focus on (nearly) solvable models of metal-metal transition in random systems. The t-J model with random and all-to-all hopping and exchange can be mapped onto a quantum impurity model coupled self-consistently to an environment (the mapping also applies to a t-J model in a large dimension lattice,  with random nearest-neighbor exchange). Such models will be argued to exhibit metal-metal quantum phase transitions in the universality class of the SYK model, accompanied by a linear-in-T resistivity from time reparameterization  fluctuations. I will also present the results of exact diagonalization of random t-J clusters, obtained recently with Henry Shackleton, Alexander Wietek, and Antoine Georges.
12:00 – 2:30pm ET
Inna Vishik (University of California, Davis)Title: Universality vs materials-dependence in cuprates: ARPES studies of the model cuprate Hg1201

Abstract: The cuprate superconductors exhibit the highest ambient-pressure superconducting transition temperatures (T c ), and after more than three decades of extraordinary research activity, continue to pose formidable scientific challenges. A major experimental obstacle has been to distinguish universal phenomena from materials- or technique-dependent ones. Angle-resolved photoemission spectroscopy (ARPES) measures momentum-dependent single-particle electronic excitations and has been invaluable in the endeavor to determine the anisotropic momentum-space properties of the cuprates. HgBa 2 CuO 4+d (Hg1201) is a single-layer cuprate with a particularly high optimal T c and a simple crystal structure; yet there exists little information from ARPES about the electronic properties of this model system. I will present recent ARPES studies of doping-, temperature-, and momentum-dependent systematics of near-nodal dispersion anomalies in Hg1201. The data reveal a hierarchy of three distinct energy scales which establish several universal phenomena, both in terms of connecting multiple experimental techniques for a single material, and in terms of connecting comparable spectral features in multiple structurally similar cuprates.
9/30/2020Jordan Cotler (Harvard)TBA
10/1/2020Omri Golan (Weizmann Institute of Science)TBA
10/7/2020Romain Vasseur (UMass Amherst)TBA
10/8/2020Justin Kulp (Perimeter Institute)TBA
10/14/2020Yin-Chen He (Perimeter Institute)TBA
10/15/2020Louis Taillefer (University of Sherbrooke)TBA
10/21/2020Oleg Dubinkin (University of Illinois at Urbana–Champaign)TBA
10/22/2020Paul Fendley (University of Oxford)TBA
10/28/2020Patrick Lee (MIT)TBA
10/29/2020Biao Lian (Princeton University)TBA
11/4/2020Zhi-Xun Shen (Stanford University)TBA
11/5/2020Zohar Ringel (Racah Institute of Physics)TBA
11/11/2020Abhishodh Prakash (ICTS)TBA
11/12/2020Chandra Varma (University of California, Riverside)TBA
11/18/2020Antoine Georges (Collège de France)TBA
11/19/2020Eduardo Fradkin (University of Illinois at Urbana-Champaign)TBA
11/25/2020Qimiao Si (Rice University)TBA
12/2/2020Andrey Chubukov (University of Minnesota)TBA
12/3/2020David B. Kaplan  (Univ Washington)
12/9/2020David Hsieh (Caltech)TBA
12/10/2020Xinan Zhou (Princeton PCTS)TBA
12/16/2020Zheng-Yu Weng (Tsinghua University)TBA

Spring 2021:

1/20/2021Thomas Peter Devereaux (Stanford University)TBA
1/27/2021Luigi Tizzano  (SCGP)TBA
5/12/2021André-Marie Tremblay (University of Sherbrooke)TBA

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