We study the dissipative dynamics of a two-level system (TLS) exposed to
strong ac driving. By combing Floquet theory with Van Vleck perturbation theory
in the TLS tunneling matrix element, we diagonalize the time-dependent
Hamiltonian and provide corrections to the renormalized Rabi frequency of the
TLS, which are valid for both a biased and unbiased TLS and go beyond the known
high-frequency and rotating-wave results. In order to mimic environmental
influences on the TLS, we couple the system weakly to a thermal bath and solve
analytically the corresponding Floquet-Bloch-Redfield master equation. We give
a closed expression for the relaxation and dephasing rates of the TLS and
discuss their behavior under variation of the driving amplitude. Further, we
examine the robustness of coherent destruction of tunneling (CDT) and
driving-induced tunneling oscillations (DITO). We show that also for a moderate
driving frequency an almost complete suppression of tunneling can be achieved
for short times and demonstrate the sensitiveness of DITO to a change of the
external parameters.Comment: 21 pages, 18 figures; published versio
