Effects of periodic driving on asymmetric two-level systems coupled to dissipative environments

We study the dynamics of intially localized states in biased dissipative TLSs evolving under a time periodic force simulating monochromatic light. Accurate numerical calculations are presented using an iterative procedure to evaluate realtime path integrals. In the high-temperature and moderate to high friction regime, the system exhibits exponential decay. In this regime the decay constant approaches a plateau value that depends only on the intensity of the driving field. Simple analytical calculations using a Landau-Zener approach predict correctly the value of the decay rate. Bias does not affect significantly the plateau value of the decay constant provided that the asymmetry is small relative to the amplitude of the driving field. In the low-friction regime, phase relations are important and there is nonmonotonic variation of the delocalization rate. Weak friction broadens the window for extending the lifetime of localized states. At very strong friction the decay rate diminishes monotonically.