Condensed matter physics is the branch of physics that studies systems of very large numbers of particles in a condensed state, like solids or liquids. Condensed matter physics wants to answer questions like: why is a material magnetic? Or why is it insulating or conducting? Or new, exciting questions like: what materials are good to make a reliable quantum computer? Can we describe gravity as the behavior of a material? The behavior of a system with many particles is very different from that of its individual particles. We say that the laws of many body physics are emergent or collective. Emergence explains the beauty of physics laws.
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Quantum States of Matter with Fractal Symmetries: Theory and realization with Rydberg atoms
Cenke Xu University of California


Measurementinduced criticality and chargesharpening transitions
Romain Vasseur University of Massachusetts Amherst



PSI Lecture  Condensed Matter  Lecture 1
Aaron Szasz Lawrence Berkeley National Laboratory (LBNL)

Quantum Criticality: Gauge Fields and Matter
27 talksCollection Number C22009Talk

Quantum Criticality in the 2+1d Thirring Model
Simon Hands University of Liverpool

(Multi)Critical Point, and Potential Realization with infinite Fractal Symmetries
Cenke Xu University of California




Fractionalized fermionic quantum criticality
Lukas Janssen Technische Universität Dresden

Bootstrapping critical gauge theories
YinChen He Perimeter Institute for Theoretical Physics

Multiband superconductivity and the breaking of time reversal symmetry
Igor Herbut Simon Fraser University (SFU)


International Workshop on Quantum Spin Ice
20 talksCollection Number C17022Talk


Anomalous transport property in the nodal metallic spin ice Pr2Ir2O7
Akito Sakai University of Tokyo



Frustrating quantum spin ice: a tale of three spin liquids and hidden order
Nicholas Shannon Okinawa Institute of Science and Technology (OIST)



Dipolar spin ice states with fast monopole hopping rate in the spinels CdEr2X4 (X=Se,S)
Tom Fennell Paul Scherrer Institute (PSI)


Quantum Machine Learning
21 talksCollection Number C16017Talk

Quantum algorithm for topological analysis of data
Seth Lloyd Massachusetts Institute of Technology (MIT)  Center for Extreme Quantum Information Theory (xQIT)



Learning Thermodynamics with Boltzmann Machines
Giacomo Torlai Flatiron Institute

Machine Learning Phases of Matter
Juan Carrasquilla Vector Institute for Artificial Intelligence


Finding density functionals with machinelearning
Kieron Burke University of California  Irvine (UCI)  Department of Physics and Astronomy

Quantum Crystals, Quantum Computing and Quantum Cognition
Matthew Fisher Kavli Institute for Theoretical Physics (KITP)


Tensor Networks for Quantum Field Theories II
18 talksCollection Number C17011Talk

Hyperinvariant tensor networks and holography
Glen Evenbly Georgia Institute of Technology

Tensor network and (padic) AdS/CFT
LingYan Hung Tsinghua University

Dynamics for holographic codes
Tobias Osborne Leibniz Universität Hannover

Random tensor networks and holographic coherent states
Xiaoliang Qi Stanford University


Complexity, Holography & Quantum Field Theory
Robert Myers Perimeter Institute for Theoretical Physics

Two Continous Approaches to AdS/Tensor Network duality
Tadashi Takayanagi Yukawa Institute for Theoretical Physics

Tensor Networks and Holography
James Sully McGill University


Low Energy Challenges for High Energy Physicists II
21 talksCollection Number C16019Talk


Bootstrapping 3D CFTs
David Poland Yale University

Universal features of Lifshitz Green’s functions from holography and field theory
Kai Sun University of Michigan


Generalized Global Symmetries and Magnetohydrodynamics
Diego Hofman Universiteit van Amsterdam

Effective field theory of dissipative fluids
Hong Liu Massachusetts Institute of Technology (MIT)  Department of Physics

Hydrodynamic electron transport in a graphene field effect transistor
Marco Polini Istituto Italiano de Technolgia

Theories of nonFermi liquids
Subir Sachdev Harvard University


An Exact Map Between the TBG (and multilayers) and Topological Heavy Fermions
Bogdan Bernevig Princeton University
Magicangle (θ=1.05∘) twisted bilayer graphene (MATBG) has shown two seemingly contradictory characters: the localization and quantumdotlike behavior in STM experiments, and delocalization in transport experiments. We construct a model, which naturally captures the two aspects, from the BistritzerMacDonald (BM) model in a first principle spirit. A set of local flatband orbitals (f) centered at the AAstacking regions are responsible to the localization. A set of extended topological conduction bands (c), which are at small energetic separation from the local orbitals, are responsible to the delocalization and transport. The topological flat bands of the BM model appear as a result of the hybridization of f and celectrons. This model then provides a new perspective for the strong correlation physics, which is now described as strongly correlated felectrons coupled to nearly free topological semimetallic celectrons  we hence name our model as the topological heavy fermion model. Using this model, we obtain the U(4) and U(4)×U(4) symmetries as well as the correlated insulator phases and their energies. Simple rules for the ground states and their Chern numbers are derived. Moreover, features such as the large dispersion of the charge ±1 excitations and the minima of the charge gap at the Γ point can now, for the first time, be understood both qualitatively and quantitatively in a simple physical picture. Our mapping opens the prospect of using heavyfermion physics machinery to the superconducting physics of MATBG. All the model’s parameters are analytically derived.

Quantum States of Matter with Fractal Symmetries: Theory and realization with Rydberg atoms
Cenke Xu University of California
In recent years, generalizations of the notion of symmetry have significantly broadened our view on states of matter. We will discuss some recent progress of understanding and realizing the "fractal symmetry", where the symmetric charge i.e. the generator of the symmetry is defined on a fractal subset of the system with a noninteger or more generally irrational Hausdorff dimension. We will introduce a series of models with exotic fractal symmetries, which can in general be deduced from a "Pascal Triangle" (also called Yang Hui Triangle in ancient China) symmetry. We will discuss their various features including quantum phase transitions. We will also discuss the potential realization of these phases and phase transitions in experimental systems, such as the highly tunable platform of Rydberg atoms.
Zoom Link: https://pitp.zoom.us/meeting/register/tJcqcihqzMvHdWYBm7mYd_XP9Amhypv5vO

Toward realization of novel superconductivity based on twisted van der Waals Josephson junction in Cuprates
Philip Kim Columbia University
Twisted interfaces between stacked van der Waals Cuprate crystals enable tunable Josephson coupling, utilizing anisotropic superconducting order parameters. Employing a novel cryogenic assembly technique, we fabricate hightemperature Josephson junctions with an atomically sharp twisted interface between Bi_2Sr_2CaCu_2O_{8+x} crystals. The critical current density J_c sensitively depends on the twist angle. While near 0 degree twist, J_c nearly matches that of intrinsic junctions, it is suppressed almost 2orders of magnitude but remained finite near 45 degree. J_c also exhibits nonmonotonic behavior versus temperature due to competition between two supercurrent contributions from nodal and antinodal regions of the Fermi surface. Near 45 degree twist angle, we observe twoperiod Fraunhofer interference patterns and fractional Shapiro steps at half integer values, a signature of cotunneling Cooper pairs necessary for high temperature topological superconductivity.
Zoom Link: https://pitp.zoom.us/meeting/register/tJcqcihqzMvHdWYBm7mYd_XP9Amhypv5vO

Measurementinduced criticality and chargesharpening transitions
Romain Vasseur University of Massachusetts Amherst
Monitored quantum circuits (MRCs) exhibit a measurementinduced phase transition between arealaw and volumelaw entanglement scaling. In this talk, I will argue that MRCs with a conserved charge additionally exhibit two distinct volumelaw entangled phases that cannot be characterized by equilibrium notions of symmetrybreaking or topological order, but rather by the nonequilibrium dynamics and steadystate distribution of charge fluctuations. These include a chargefuzzy phase in which charge information is rapidly scrambled leading to slowly decaying spatial fluctuations of charge in the steady state, and a chargesharp phase in which measurements collapse quantum fluctuations of charge without destroying the volumelaw entanglement of neutral degrees of freedom. I will present some statistical mechanics and effective field theory approaches to such chargesharpening transitions.
Zoom Link: https://pitp.zoom.us/meeting/register/tJcqcihqzMvHdWYBm7mYd_XP9Amhypv5vO

Ultra Unification: Quantum Criticality and Deformation beyond the Standard Model
Juven Wang Harvard University
We introduce a viewpoint that the Standard Model (SM) is a lowenergy quantum vacuum arising from various neighbor Grand Unification (GUT) like vacua competition in an immense quantum phase diagram. In general, we find the SM arises near the gapless quantum critical regions between the competing neighbor vacua. Alternatively, we can also phrase this viewpoint in terms of the deformation class of quantum field theory (QFT), specified by its symmetry G and its anomaly (i.e., cobordism invariant). Seemly different QFTs of the same deformation class can be deformed to each other via quantum phase transitions. We show that GUT such as GeorgiGlashow su(5), PatiSalam su(4)×su(2)×su(2), Barr’s flipped u(5), and familiar or modified so(n) models of Spin(n) gauge group, e.g., with n = 10, 18 can all reside in an appropriate SM deformation class, labeled by Z_{16} and Z_2 nonperturbative global anomaly index. We show that Ultra Unification, which replaces some of sterile neutrinos with new exotic gapped/gapless sectors (e.g., topological or conformal field theory) or gravitational sectors with topological origins via cobordism constraints, also resides in an SM deformation class. Neighbor quantum phases near SM or their phase transitions, and neighbor gauge enhanced gapless quantum criticality naturally exhibit beyond SM phenomena. We give a new proposal on the neutrino mass origin. The talk is mainly based on: arxiv 1910.14668, 2006.16996, 2008.06499, 2012.15860, 2106.16248, 2111.10369, 2112.14765. Some of these works are in collaboration with Zheyan Wan and YiZhuang You.
Zoom Link: https://pitp.zoom.us/j/94634619703?pwd=VWlWZHNIMm1sS2owWnlhSmhZTTNvUT09

Getting the most out of your measurements: neural networks and active learning
Annabelle Bohrdt Harvard University
Recent advances in quantum simulation experiments have paved the way for a new perspective on strongly correlated quantum manybody systems. Digital as well as analog quantum simulation platforms are capable of preparing desired quantum states, and various experiments are starting to explore nonequilibrium manybody dynamics in previously inaccessible regimes in terms of system sizes and time scales. Stateofthe art quantum simulators provide singlesite resolved quantum projective measurements of the state. Depending on the platform, measurements in different local bases are possible. The question emerges which observables are best suited to study such quantum manybody systems.
In this talk, I will cover two different approaches to make the most use of these possibilities. In the first part, I will discuss the use of machine learning techniques to study the thermalization behavior of an interacting quantum system. A neural network is trained to distinguish nonequilibrium from thermal equilibrium data, and the network performance serves as a probe for the thermalization behavior of the system. We apply this method to numerically simulated data, as well experimental snapshots of ultracold atoms taken with a quantum gas microscope.
In the second part of this talk, I will present a scheme to perform adaptive quantum state tomography using active learning. Based on an initial, small set of measurements, the active learning algorithm iteratively proposes the basis configurations which will yield the maximum information gain. We apply this scheme to GHZ states of a few qubits as well as ground states of onedimensional lattice gauge theories and show an improvement in accuracy over random basis configurations.

PSI Lecture  Condensed Matter  Lecture 1
Aaron Szasz Lawrence Berkeley National Laboratory (LBNL)

Quantum Criticality: Gauge Fields and Matter
27 talksCollection Number C22009Quantum Criticality: Gauge Fields and Matter 
International Workshop on Quantum Spin Ice
20 talksCollection Number C17022International Workshop on Quantum Spin Ice


Tensor Networks for Quantum Field Theories II
18 talksCollection Number C17011Tensor Networks for Quantum Field Theories II 
Low Energy Challenges for High Energy Physicists II
21 talksCollection Number C16019Low Energy Challenges for High Energy Physicists II