Critical relaxation with overdamped quasiparticles in open quantum systems

TL;DR

This paper investigates the late-time relaxation dynamics in an open quantum system, revealing a crossover from exponential to power-law decay near a dynamical phase transition, with implications for ultracold atom experiments.

Contribution

It provides a detailed analysis of relaxation processes and quasiparticle behavior in the open Dicke model near criticality, highlighting the interplay between dissipation and intrinsic interactions.

Findings

Power-law relaxation driven by quasiparticle collisions near criticality

Finite quasiparticle lifetime prevents aging phenomena

Crossover from exponential to power-law decay observed

Abstract

We study the late-time relaxation following a quench in a driven-dissipative quantum many-body system. We consider the open Dicke model, describing the infinite-range interactions between $N$ atoms and a single, lossy electromagnetic mode. We show that the dynamical phase transition at a critical atom-light coupling is characterized by the interplay between reservoir-driven and intrinsic relaxation processes. Above the critical coupling, small fluctuations in the occupation of the dominant quasiparticle-mode start to grow in time while the quasiparticle lifetime remains finite due to losses. Near the critical interaction strength we observe a crossover between exponential and power-law $1/\tau$ relaxation, the latter driven by collisions between quasiparticles. For a quench exactly to the critical coupling, the power-law relaxation extends to infinite times, but the finite lifetime of quasiparticles prevents ageing to appear. We predict our results to be accessible to quench experiments with ultracold bosons in optical resonators.