Coherent exciton dynamics in a dissipative environment maintained by an off-resonant vibrational mode

TL;DR

This paper investigates how strong coupling to a single vibrational mode influences the coherence of a two-level quantum system within a structured environment, revealing spectral density-dependent modifications to its dynamics.

Contribution

It provides an exact treatment of a single vibrational mode coupled to a two-level system and analyzes how this affects coherence in different environmental spectral densities.

Findings

Coupling causes a renormalization of the oscillation frequency.

Coherent behaviour can be enhanced or suppressed depending on spectral density.

An analytical model explains the observed modifications.

Abstract

The interplay between an open quantum system and its environment can lead to both coherent and incoherent behaviour. We explore the extent to which strong coupling to a single bosonic mode can alter the coherence properties of a two-level system in a structured environment. This mode is treated exactly, with the rest of the environment comprising a Markovian bath of bosonic modes. The strength of the coupling between the two-level system and the single mode is varied for a variety of different forms for the bath spectral density in order to assess whether the coherent dynamics of the two-level system are modified. We find a clear renormalisation of the site population oscillation frequency that causes an altered interaction with the bath. This leads to enhanced or reduced coherent behaviour of the two-level system depending on the form of the spectral density function. We present an intuitive interpretation, based on an analytical model, to explain the behaviour.