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TT: Fachverband Tiefe Temperaturen

TT 69: Nonequilibrium Quantum Systems II (joint session TT/DY)

TT 69.1: Talk

Thursday, March 21, 2024, 09:30–09:45, H 3025

Nontrivial damping of quantum many-body dynamics in the spin-1/2 XXZ chain — •Mariel Kempa and Robin Steinigeweg — U Osnabrück, Germany

Understanding how the dynamics of a given quantum system with many degrees of freedom is altered by the presence of a generic perturbation is a notoriously difficult question. Recent works predict that, in the overwhelming majority of cases, the unperturbed dynamics is just damped by a simple function, e.g., exponentially as expected from Fermi’s golden rule. While these predictions rely on random-matrix arguments and typicality, they can only be verified for a specific physical situation. It also remains unclear how frequent and under which conditions counterexamples to the typical behavior occur. We address this question from the perspective of projection-operator techniques, where exponential damping of a density matrix occurs in the interaction picture but not necessarily in the Schrödinger picture. We show that a nontrivial damping in the Schrödinger picture can emerge if the dynamics in the unperturbed system possesses rich features, for instance due to the presence of strong interactions. We substantiate our theoretical arguments by large-scale numerical simulations of spin transport in a perturbed spin-1/2 XXZ chain.

[1] T. Heitmann et al., Phys. Rev. E 104 (2021) 054145

[2] M. Kempa et al., in preparation

Keywords: spin systems; correlation functions; quantum systems; perturbation theory