Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session K49: Precision Many-Body Physics IV: DynamicsFocus Recordings Available
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Sponsoring Units: DCOMP DAMOP DCMP Chair: Utkarsh Agrawal, University of Massachusetts, Amherst Room: McCormick Place W-471B |
Tuesday, March 15, 2022 3:00PM - 3:36PM |
K49.00001: Quantum fluctuations of the out-of-equilibrium one-dimensional Bose gas described by Generalized Hydrodynamics Invited Speaker: JEROME DUBAIL Agence National de la Recherche - project QUADY - ANR-20-CE30-0017-01 |
Tuesday, March 15, 2022 3:36PM - 3:48PM |
K49.00002: Average entanglement entropy at late times Rishabh Kumar, Eugenio Bianchi The average entanglement entropy of a random pure state was determined by Page in 1993. Here we consider an isolated quantum system and study the behavior of the entanglement entropy at late times. We assume that the system is initially in a non-entangled state. We show that, for a random-matrix Hamiltonian, we recover the Page average and estimate the size of the fluctuations around the average. We derive also analogous results for random quadratic fermionic systems. The result is of interest for the analysis of thermalization in isolated quantum systems. |
Tuesday, March 15, 2022 3:48PM - 4:00PM |
K49.00003: Addressing quantum embedding via the algorithmic inversion of dynamical potentials Tommaso Chiarotti, Nicola Marzari, Andrea Ferretti Quantum embedding formulations are used to describe physical systems immersed in a bath. Frequency-dependent potentials are needed to couple the two systems and appear in embedding formalisms such as many-body perturbation theory, dynamical mean-field theory, electron-boson coupling, or spectral potentials. Once formulated (e.g., via. many-body perturbation theory), the solution at all frequencies of non-linear-Dyson-like equations is needed to retrieve spectral and thermodynamic quantities for the system studied. Here we apply the algorithmic inversion method to solve exactly and at all frequencies Dyson-like equations for homogeneous systems, with application to the homogeneous electron gas, and discuss the extension to non-homogeneous systems. |
Tuesday, March 15, 2022 4:00PM - 4:12PM |
K49.00004: Analytic continuation of the imaginary-frequency Green's function via causal smoothing spline approach Mancheon Han, Hyoung Joon Choi Many of practical many-body calculations are conducted in imaginary time and frequency. To obtain dynamic physical quantities such as electronic spectral functions, we need to obtain real-frequency Green's functions from imaginary-frequency Green's functions. This procedure is known as the analytic continuation, and it is known to be ill-posed. In this work, we suggest a causal smoothing spline approach for the analytic continuation. Our causal smoothing spline approach discretizes the problem by using the cubic spline on nonuniformly generated real-frequency grids and regularizes the ill-posedness by using the second derivatives of the spectral function. We determine the regularization parameter by balancing the regularization with data fit. As a result, our approach conducts the analytic continuation stably with few control parameters, and it can be applied straightforwardly to matrix-valued Green's functions as well. By applying it to systems of known spectral functions, we demonstrate that our approach is robust and precise. Moreover, we show the use of our causal smoothing spline approach in dynamical mean-field theory calculations. |
Tuesday, March 15, 2022 4:12PM - 4:24PM |
K49.00005: Conservation laws in coupled cluster dynamics at finite-temperature Ruojing Peng, Alec F White, Huanchen Zhai, Garnet Chan We extend the finite-temperature Keldysh non-equilibrium coupled cluster theory (Keldysh-CC) [A. F. White and G. K.-L. Chan, J. Chem. Theory Comput. 15, 6137–6253 (2019)] to include a time-dependent orbital basis. When chosen to minimize the action, such a basis restores local and global conservation laws (Ehrenfest’s theorem) for all one-particle properties while remaining energy conserving for time-independent Hamiltonians. We present the time-dependent Keldysh orbital-optimized coupled cluster doubles method in analogy with the formalism for zero-temperature dynamics, extended to finite temperatures through the time-dependent action on the Keldysh contour. To demonstrate the conservation property and understand the numerical performance of the method, we apply it to several problems of non-equilibrium finite-temperature dynamics: a 1D Hubbard model with a time-dependent Peierls phase, laser driving of molecular H2, driven dynamics in warm-dense silicon, and transport in the single impurity Anderson model. |
Tuesday, March 15, 2022 4:24PM - 5:00PM |
K49.00006: High order perturbative methods for out of equilibrium quantum many-body systems. Quantum quasi-Monte Carlo and beyond. Invited Speaker: Olivier P Parcollet I will review some recent developments of numerically exact approaches based on |
Tuesday, March 15, 2022 5:00PM - 5:12PM |
K49.00007: Quantum Quasi-Monte Carlo algorithm for out-of-equilibrium Green functions at long times. Corentin Bertrand, Philipp Dumitrescu, Marjan Maček, Olivier P Parcollet, Daniel Bauernfeind, Xavier Waintal The Quantum Quasi-Monte Carlo (QQMC) algorithm allows to compute observables in a system of strongly correlated fermions driven out of equilibrium by an external time-dependent field or a voltage bias. It can produce non perturbative results, and its computational cost is independent of time after a quench. Potential applications are numerous, ranging from the design of nanoelectronic devices, to transport properties of correlated materials, or even the characterization of quantum chaos. We will show how using quasi-Monte Carlo improved its performances compared to previous Markov-chain Monte Carlo, and illustrate with applications. |
Tuesday, March 15, 2022 5:12PM - 5:24PM |
K49.00008: Quantum Many-body Dynamics in a Squeezing-while-rotating Scheme Zeyang Li, Simone Colombo, Edwin Pedrozo Penafiel, Chi Shu, Mikhail Lukin, Vladan Vuletic An ensemble of atomic spin interacting with an optical cavity mode is widely studied and attracts many interests from quantum metrology to quantum many-body physics. The optical cavity can generate a coherent long-ranged spin-spin interaction among atomic ensembles via the one-axis twisting Hamiltonian. The dynamics of the spin system are significantly affected and exhibit rich quantum many-body phenomena by exposing the ensemble to an additional transverse field. In addition, by using a recently achieved time-reversal toolbox, one also has a probe of more non-trivial collective spin states, especially those with high quantum Fisher information. We will report here our experimental and theoretical progress in this direction and an outlook for exploring other exotic quantum properties. |
Tuesday, March 15, 2022 5:24PM - 5:36PM |
K49.00009: Measuring post-quench entanglement entropy through density correlations Adrian G Del Maestro, Bernd Rosenow, Hatem Barghathi Following an interaction quench in an integrable system of one-dimensional fermions, we analyze the dependence of the density-density correlation function on the observation time. Using the fact that for small waiting times every one-dimensional system can be bosonized in the high-energy sector, we extract bosonic occupation numbers from the density-density correlation function, and use them to compute the bosonic entropy from an effective diagonal ensemble. Inspired by the connection between the Yang-Yang and entanglement entropy in quenched integrable quantum systems, we compare the bosonic entropy with the steady state spatial entanglement entropy per particle computed via exact diagonalization and find excellent agreement. This result provides a route to the experimental measurement of entanglement in closed quantum systems without the use of a replicated Hilbert space, and could be confirmed via Bragg spectroscopy of integrable (or nearly integrable) ultracold atom systems. |
Tuesday, March 15, 2022 5:36PM - 5:48PM |
K49.00010: Simulating quantum many-body dynamics on noisy intermediate-scale quantum devices with typicality Jonas Richter, Arijeet Pal In a recent milestone experiment, Google's processor Sycamore heralded the era of "quantum supremacy" by sampling from the output of (pseudo-)random circuits. By leveraging the concept of quantum typicality (QT), we show that such random circuits provide tailor-made building blocks for simulating the dynamics of quantum many-body systems on noisy intermediate-scale quantum (NISQ) devices. QT can be understood as a form of quantum parallelism and asserts that even a single quantum state, drawn at random from a high-dimensional Hilbert space, can mimic the properties of the full statistical ensemble. Here, we propose a QT-based algorithm consisting of a random circuit followed by a trotterized Hamiltonian time evolution to simulate hydrodynamics and study transport properties in the linear response regime, which we numerically exemplify for one- and two-dimensional quantum spin systems. While the algorithm operates without an overhead of bath or ancilla qubits for initial-state preparation and measurement, our numerics further suggest that it is comparatively robust against systematic Trotter errors and noisy gates. Our work emphasizes the practical relevance of random circuits on NISQ devices beyond the abstract sampling task. |
Tuesday, March 15, 2022 5:48PM - 6:00PM |
K49.00011: Exact results for nonlinear Drude weights in the spin-1/2 XXZ chain Yuhi Tanikawa, Kazuaki Takasan, Hosho Katsura Nonlinear Drude weight (NLDW) is a generalization of the linear Drude weight [1], which characterizes the nonlinear transport in quantum many-body systems. We investigate these weights for the spin-1/2 XXZ chain in the critical regime at zero temperature [2,3]. The analysis of the NLDWs based on the Bethe ansatz reveals that they exhibit convergence, power-law, and logarithmic divergence with system size, depending on the anisotropy parameter Δ. The divergence occurs in all orders and can be regarded as a generic feature of the NLDWs. We study the origin of the divergences and find that they result from nonanalytic finite-size corrections to the ground state energy. Furthermore, for the convergent cases, we compute closed-form expressions for several weights in the thermodynamic limit by using the Wiener-Hopf method. |
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