Non-Markovian decoherence of a two-level system in a Lorentzian bosonic reservoir and a stochastic environment with finite correlation time

TL;DR

This paper explores the non-Markovian dynamics of a two-level quantum system interacting with a Lorentzian bosonic reservoir and a stochastic environment, analyzing steady states, spectral properties, and the effects of approximations.

Contribution

It introduces a numerically exact hierarchical equations of motion approach to study complex non-Markovian effects in a combined quantum and stochastic environment.

Findings

Steady states depend on frequency cutoffs and coupling strengths.

Non-Markovian dynamics significantly influence the system's evolution.

The rotation-wave approximation impacts the accuracy of the results.

Abstract

In this paper we investigate non-Markovian evolution of a two-level system (qubit) in a bosonic bath under influence of an external classical fluctuating environment. The interaction with the bath has the Lorentzian spectral density, and the fluctuating environment (stochastic field) is represented by a set of Ornstein-Uhlenbeck processes. Each of the subenvironments of the composite environment is able to induce non-Markovian dynamics of the two-level system. By means of the numerically exact method of hierarchical equations of motion, we study dependence of the steady states of the two-level system, the reduced density matrix evolution and the equilibrium emission spectrums on frequency cutoffs and coupling strengths of the subenvironments. Additionally we investigate the impact of the rotation-wave approximation (RWA) used for the interaction with the bath on accuracy of the results.