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 Many-Body 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: T-linear resistivity and spectroscopy of hot metals and cold atoms: DMFT, SYK and beyond Invited Speaker: Antoine Georges Many materials with strong electronic correlations display metallic-like resistivity up to |
Tuesday, March 3, 2020 3:06PM - 3:18PM |
J43.00002: SYK non-Fermi-liquid solution of the Hubbard model Aaram J. Kim, Philipp Werner, Evgeny Kozik The bold-line diagrammatic technique solution of the Hubbard model in the strong coupling regime is of an SYK non-Fermi-liquid (nFL) type, obtained in a controlled way by the numerically exact diagrammatic Monte Carlo method. In the atomic (zero-hopping) limit, the solution corresponds to the unphysical branch of the Luttinger-Ward 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 SYK-type nFL regime in a wide intermediate temperature range enclosed by the low-temperature Fermi-liquid and the high-temperature 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 Schrieffer-Wolff Transformations for Quantum Many-body 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 Schrieffer-Wolff 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 non-equilibrium many-body 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 non-integrable quantum many-body systems with sub-exponential computational effort Pavan Hosur Non-integrable 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 few-point 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 non-integrable systems with sub-exponential 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 time-crystallization effects in multicomponent superfluids Boris Svistunov, Nikolai Prokof'ev We observe that space- and time-crystallization effects in multicomponent superfluids—while having the same physical origin and mathematical description as in the single-component 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 two-component counterflow |
Tuesday, March 3, 2020 3:54PM - 4:06PM |
J43.00006: A generic quantum Monte Carlo approach for electronic correlations in out-of-equilibrium systems. Corentin Bertrand, Serge Florens, Olivier Parcollet, Xavier Waintal We propose a systematic approach to the non-equilibrium 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 Schwinger-Keldysh perturbation theory and uses numerical resummation to obtain spectral functions directly in real time. We show that even non-Fermi 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 spin-boson model using real-time quantum Monte Carlo Olga Goulko, Guy Cohen, Moshe Goldstein, Hsing-Ta Chen We present results for the real-time dynamics of the spin-boson model (a two-state system coupled to a bath of non-interacting harmonic modes) using the inchworm Monte Carlo algorithm. In particular, we study the population difference between the two states at strong system-bath coupling. We focus on sub-Ohmic 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 Many-Body 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: Time-symmetric stochastic action in curved phase-space Peter Drummond, Margaret Reid, Ria Rushin Joseph Quantum field dynamics is equivalent to a forward-backward stochastic process in both time directions, and can be calculated from an equilibration in a fifth space-time dimension [1]. Stochastic time-symmetric action principles in a curved phase-space 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 many-body 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 time-dimension 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 wave-function collapse. |
Tuesday, March 3, 2020 4:54PM - 5:06PM |
J43.00011: Bounding the finite-size error for simulations of quantum many-body 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 locally-interacting systems, as well as in real time quench dynamics simulations initiated from a product state. The key step of our method relies on the well-known Lieb-Robinson (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 finite-temperature many-body physics Gaurav Harsha, Thomas M Henderson, Gustavo E Scuseria Wave function methods are widely used to study ground-state properties of many-electron 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 field-theoretical tool to study non-equilibrium 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 finite-temperature generalizations of ground-state 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, Andre-Marie 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 DC-conductivity. We explore various modern architectures of neural network and various tailored-made loss functions for this problem. |
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