Quantum master equations and steady states for the ultrastrong-coupling limit and the strong-decoherence limit

TL;DR

This paper derives quantum master equations applicable in the ultrastrong-coupling and strong-decoherence regimes, revealing conditions under which the mean force Gibbs state remains stationary, thus advancing the understanding of open quantum system dynamics.

Contribution

It introduces generalized master equations for regimes with ultrastrong coupling and strong decoherence, extending existing theories like Foerster and Redfield.

Findings

Master equations valid in ultrastrong-coupling regime

Mean force Gibbs state is stationary in these regimes

Generalization of Foerster and Redfield theories

Abstract

In the framework of theory of open quantum systems, we derive quantum master equations for the ultrastrong system-bath coupling regime and, more generally, the strong-decoherence regime. In this regime, the strong decoherence is complemented by slow relaxation processes. We use a generalization of the Foerster and modified Redfield peturbation theories known in theory of excitation energy transfer. Also, we show that the mean force Gibbs state in the corresponding limits are stationary for the derived master equations.