The reduced dynamics of an exciton coupled to a phonon bath: A new approach combining the Lang-Firsov transformation and the perturbation theory

摘要

To go beyond the Born approximation, a new method is introduced for describing the reduced dynamics of an exciton coupled to a phonon bath. Two unitary transformations are applied for accounting for the exciton-phonon entanglement through a dual dressing mechanism affecting both the exciton and the phonons. In doing so, one obtains an analytical expression of the exciton reduced density matrix without integrating numerically any generalized master equation. Therefore, by using a quite simple model that can be solved exactly, it has been shown that the proposed method is particularly suitable for describing the exciton dynamics over a rather broad region in the parameter space. However, although the method shows many strengths, it also exhibits weaknesses and it accidentally breaks down owing to the occurrence of specific resonances.