Effective thermodynamics of strongly coupled qubits

TL;DR

This paper investigates how entanglement affects the thermal behavior of strongly coupled qubits and proposes an effective temperature concept to restore thermal laws in such quantum systems.

Contribution

It introduces the idea of an effective temperature for strongly coupled qubits, enabling a pseudo-thermal description despite entanglement-induced violations.

Findings

Effective temperature can be defined for two-state systems.

Numerical analysis supports the pseudo-thermal state concept.

Entanglement prevents true thermalization in strongly coupled systems.

Abstract

Interactions between a quantum system and its environment at low temperatures can lead to violations of thermal laws for the system. The source of these violations is the entanglement between system and environment, which prevents the system from entering into a thermal state. On the other hand, for two-state systems, we show that one can define an effective temperature, placing the system into a `pseudo-thermal' state where effective thermal laws are upheld. We then numerically explore these assertions for an n-state system inspired by the spin-boson environment.