Quantum Thermalization beyond Non-Integrability and Quantum Scars in a Multispecies Bose-Josephson Junction

TL;DR

This study explores quantum thermalization in a three-species Bose-Josephson Junction, revealing that thermalization can occur in both chaotic and integrable regimes, and identifying quantum scars as non-thermalizing states.

Contribution

It demonstrates that non-integrability is not necessary for thermalization and characterizes quantum scars in a multispecies BJJ system.

Findings

Thermalization occurs in both chaotic and integrable regimes.

Quantum scars are identified as non-thermalizing states in the chaotic regime.

Thermalization breaks down in the separable limit.

Abstract

This work investigates the relationship between quantum chaos and thermalization in a three-species Bose-Josephson Junction (BJJ) with mutual interactions, without coupling to any external environment. The analysis is grounded in the Eigenstate Thermalization Hypothesis (ETH), the modern framework for quantum thermalization, in which non-integrability and chaos are historically assumed as prerequisites. After a thorough characterization of quantum chaos in this system, we examine the occurrence of thermal behavior expected when ETH holds. We identify three distinct regimes: chaotic, integrable, and separable. Remarkably, quantum thermalization occurs in both the chaotic and integrable regimes, while it breaks down in the separable limit - supporting that non-integrability is not a necessary condition for thermalization. Furthermore, since the system exhibits collective phenomena in the semiclassical limit, we identify athermal states in the chaotic regime classifiable as quantum scars, which show no signs of thermalization, consistently with a weak form of ETH. These findings contribute to the understanding of ergodicity breaking, emerging statistical behavior, and non-equilibrium dynamics in ultracold many-body quantum systems.