Non-Markovian coherence dynamics of driven spin boson model: damped quantum beat or large amplitude coherence oscillation

The dynamics of driven spin boson model is studied analytically by means of the perturbation approach based on a unitary transformation. We gave the analytical expression for the population difference and coherence of the two level system. The results show that in the weak driven case, the population difference present damped coherent oscillation (single or double frequency) and the frequencies depend on the initial state. The coherence exhibit damped oscillation with Rabi frequency. When driven field is strong enough, the population difference exhibit undamped large-amplitude coherent oscillation. The results easily return to the two extreme cases without dissipation or without periodic driven.