Quantum thermalization and thermal entanglement in the open quantum Rabi model

TL;DR

This paper investigates how the open quantum Rabi model thermalizes and develops thermal entanglement under different bath configurations, revealing conditions for thermalization and quantifying entanglement across various regimes.

Contribution

It introduces a global quantum master equation approach in the eigenstate basis to analyze thermalization and entanglement in the open quantum Rabi model, covering diverse coupling and temperature regimes.

Findings

QRM thermalizes only when baths have equal temperature or only one bath is coupled.

QRM always thermalizes when coupled to a common heat bath.

Thermal entanglement quantified by logarithmic negativity across parameter space.

Abstract

We study quantum thermalization and thermal entanglement in the open quantum Rabi model (QRM), in which a two-level system and a single-mode bosonic field are coupled to either two individual heat baths or a common heat bath. By treating the QRM as an effective multilevel system and deriving global quantum master equations in the eigenstate representation of the QRM, we study the physical conditions for quantum thermalization of the open QRM. It is found that, in the individual heat-bath case, the QRM can only be thermalized when either the two heat baths have the same temperature or the QRM is only coupled to one of the two baths. In the common heat-bath case, differently, the QRM can always be thermalized. We also study thermal entanglement of the QRM in both the resonant- and non-resonant coupling cases. The logarithmic negativity for the thermal state of the QRM is obtained in a wide parameter space, ranging from the low- to high-temperature limits, and from the weak- to deep-strong-coupling regimes. This work paves the way towards the study of quantum effects in nonequilibrium ultrastrongly-coupled light-matter systems.