Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session J43: Precision ManyBody Physics V: Dynamics and Finite Temperature PropertiesFocus

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Sponsoring Units: DCOMP DAMOP DCMP Chair: Thomas Schaefer, Ecole Polytechnique Room: 702 
Tuesday, March 3, 2020 2:30PM  3:06PM 
J43.00001: Tlinear resistivity and spectroscopy of hot metals and cold atoms: DMFT, SYK and beyond Invited Speaker: Antoine Georges Many materials with strong electronic correlations display metalliclike resistivity up to 
Tuesday, March 3, 2020 3:06PM  3:18PM 
J43.00002: SYK nonFermiliquid solution of the Hubbard model Aaram J. Kim, Philipp Werner, Evgeny Kozik The boldline diagrammatic technique solution of the Hubbard model in the strong coupling regime is of an SYK nonFermiliquid (nFL) type, obtained in a controlled way by the numerically exact diagrammatic Monte Carlo method. In the atomic (zerohopping) limit, the solution corresponds to the unphysical branch of the LuttingerWard functional, for which the SYK model is the exact solution at the second order. Interestingly, the Green’s function retains its scaling form at higher orders. The solution for the doped 2d Hubbard model features an SYKtype nFL regime in a wide intermediate temperature range enclosed by the lowtemperature Fermiliquid and the hightemperature atomic limit. The possibility of SYK physics taking place in the Hubbard model is discussed. 
Tuesday, March 3, 2020 3:18PM  3:30PM 
J43.00003: Variational SchriefferWolff Transformations for Quantum Manybody Dynamics Jonathan Wurtz, Pieter W Claeys, Anatoli S Polkovnikov Building on recent results for adiabatic gauge potentials, we propose a variational approach for computing the generator of SchriefferWolff transformations, and demonstrate its accuracy in spin chains and fermionic systems. Because of their variational nature, the generator goes beyond standard perturbative regimes and has accuracy controlled by the locality of the ansatz. This allows for precision nonequilibrium manybody dynamics far from integrable regimes, and can be considered as improvements to the Truncated Spectrum Approach. 
Tuesday, March 3, 2020 3:30PM  3:42PM 
J43.00004: Investigating nonintegrable quantum manybody systems with subexponential computational effort Pavan Hosur Nonintegrable quantum systems  systems with no or few conserved quantities  are generically exponentially hard to solve. Recent developments have proven, at least for small system sizes, that these systems satisfy the eigenstate thermalization hypothesis (ETH). Specifically, their physical properties such as expectation values of simple observables and fewpoint correlation functions, depend smoothly on macroscopic variables such as the energy density, particle density etc. This behavior explains, qualitatively, how statistical mechanics and ergodicity emerges from quantum mechanical laws for such systems. In this talk, an algorithm will be presented that enables quantitative predictions based on the ETH. In particular, it can simulate finite temperature properties of nonintegrable systems with subexponential effort by exploiting the ETH. By expressing an eigenstate density matrix as truncatable series of orthogonal polynomials of the Hamiltonian, it will require only sparse matrix multiplication instead of matrix diagonalization. Moreover, it will store sparse matrices as vectors in the Fock space of operators, which reduces storage requirements from exponential to polynomial. Benchmarks between the algorithm and exact diagonalization on prototypical models will be shown. 
Tuesday, March 3, 2020 3:42PM  3:54PM 
J43.00005: Space and timecrystallization effects in multicomponent superfluids Boris Svistunov, Nikolai Prokof'ev We observe that space and timecrystallization effects in multicomponent superfluids—while having the same physical origin and mathematical description as in the singlecomponent case—are conceptually much more straightforward. Specifically, the values of the temporal and spatial periods are absolute rather than relative, and the broken translation symmetry in space and/or time can be revealed with experiments involving only one equilibrium sample. We discuss two realistic setups—one with cold atoms and another one with bilayer superconductors—or observation of space and time crystallization in twocomponent counterflow 
Tuesday, March 3, 2020 3:54PM  4:06PM 
J43.00006: A generic quantum Monte Carlo approach for electronic correlations in outofequilibrium systems. Corentin Bertrand, Serge Florens, Olivier Parcollet, Xavier Waintal We propose a systematic approach to the nonequilibrium dynamics of strongly 
Tuesday, March 3, 2020 4:06PM  4:18PM 
J43.00007: Dynamic Behavior of Strongly Coupled Quantum Dots Philipp Dumitrescu, Marjan Maček, Corentin Bertrand, Xavier Waintal, Olivier Parcollet We study a system of strongly correlated quantum dots, using a recently developed diagrammatic quantum Monte Carlo approach. Here, one calculates high orders of SchwingerKeldysh perturbation theory and uses numerical resummation to obtain spectral functions directly in real time. We show that even nonFermi liquid behavior of strongly coupled quantum dots can be revealed. We study this behavior in both equilibrium and in situations where the dots are driven by an external current. 
Tuesday, March 3, 2020 4:18PM  4:30PM 
J43.00008: Dynamical properties of the spinboson model using realtime quantum Monte Carlo Olga Goulko, Guy Cohen, Moshe Goldstein, HsingTa Chen We present results for the realtime dynamics of the spinboson model (a twostate system coupled to a bath of noninteracting harmonic modes) using the inchworm Monte Carlo algorithm. In particular, we study the population difference between the two states at strong systembath coupling. We focus on subOhmic spectral densities of the bosonic bath, where the system exhibits a second order quantum phase transition between localized and delocalized regimes. The inchworm algorithm is efficient over a wide range of temperatures (including low, intermediate, and high temperatures) and thus allows us to examine the changes in dynamics as the temperature is increased above zero and the emergence of a quantum critical fan. 
Tuesday, March 3, 2020 4:30PM  4:42PM 
J43.00009: Reconstructing Nonequilibrium Regimes of Quantum ManyBody Systems from the Analytical Structure of Perturbative Expansions Corentin Bertrand, Serge Florens, Olivier Parcollet, Xavier Waintal We present a systematic approach to the nonequilibrium dynamics of strongly 
Tuesday, March 3, 2020 4:42PM  4:54PM 
J43.00010: Timesymmetric stochastic action in curved phasespace Peter Drummond, Margaret Reid, Ria Rushin Joseph Quantum field dynamics is equivalent to a forwardbackward stochastic process in both time directions, and can be calculated from an equilibration in a fifth spacetime dimension [1]. Stochastic timesymmetric action principles in a curved phasespace are central to these results. They can be used to compute a stochastic bridge, the probability for random paths between two states, with any positive or negative diffusion. Such bridges have other precision applications, in fields ranging from manybody quantum dynamics to cell biology, control theory and finance. Numerical methods and examples of solutions to the resulting stochastic partial differential equations in a higher timedimension are obtained. These give agreement with exact solutions for bosonic quantum field dynamics, including entangled systems. This novel approach may lead to useful computational techniques, as the action principle is real. Of more fundamental significance is that it provides an ontological model of reality [2] in cosmological models, and allows an interpretation of objective measurement without wavefunction collapse. 
Tuesday, March 3, 2020 4:54PM  5:06PM 
J43.00011: Bounding the finitesize error for simulations of quantum manybody systems Zhiyuan Wang, Kaden Hazzard, Michael Feig Finite size errors are ubiquitous in numerical simulations of quantum many body systems, and an estimation of these errors is crucial to the assessment of the reliability of their results. In this talk I present rigorous upper bounds on finite size error of local observables measured in gapped ground states of locallyinteracting systems, as well as in real time quench dynamics simulations initiated from a product state. The key step of our method relies on the wellknown LiebRobinson (LR) bound, which is a direct consequence of locality. We show that the error bounds are practically useful, enabled by the recent tightening of the LR bounds [1]. For example, in a ground state simulation of the transverse field Ising model with J=1, h=2 and L=25 sites, the relative error for a center site observable is less than 2% and decays exponentially with system size. In a quench dynamics simulation of the same model, the relative error bound remains to be within 1% up to the time at which the system equilibrates, and decays superexponentially with system size at fixed time. 
Tuesday, March 3, 2020 5:06PM  5:18PM 
J43.00012: Thermofield theory for finitetemperature manybody physics Gaurav Harsha, Thomas M Henderson, Gustavo E Scuseria Wave function methods are widely used to study groundstate properties of manyelectron systems in condensed matter physics and chemistry, and have therefore seen tremendous development over the last fifty years or so. But standard wave function techniques cannot easily be used to compute thermal properties, because doing so requires the entire spectrum and the problem becomes computationally intractable. Thermofield dynamics, which has seen widespread application as a fieldtheoretical tool to study nonequilibrium properties, provides a wave function representation for the thermal density matrix. In this talk, I will present our recently developed framework (arXiv:1901.06753 and 1907.11286) which shows how the thermofield theory can be utilized to construct finitetemperature generalizations of groundstate wave function methods. I will provide an example of thermal coupled cluster theory and present results for its performance on standard electronic and spin systems. 
Tuesday, March 3, 2020 5:18PM  5:30PM 
J43.00013: Analytical continuation of transport functions with deep neural networks Simon Verret, Reza Nourafkan, Samuel Desrosiers, AndreMarie Tremblay In the last few years, deep neural networks have proved to be highly efficient tools to address the problem of analytical continuation of the Matsubara Green’s function [1,2,3,4]. Extending these tools to reconstruct spectral representation of correlation function for transport quantities would be very beneficial because for several of transport quantities, such as Hall conductivity and Seebeck effect [5,6], the spectral weight is not strictly positive, restricting the use of the maximum entropy method. In this work, we extend the use of deep neural networks to the case of the longitudinal conductivity, in particular the DCconductivity. We explore various modern architectures of neural network and various tailoredmade loss functions for this problem. 
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