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

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.