  Quantum resonant activation is investigated for the archetype setup of an
externally driven two-state (spin-boson) system subjected to strong dissipation
by means of both analytical and extensive numerical calculations. The
phenomenon of resonant activation emerges in the presence of either randomly
fluctuating or deterministic periodically varying driving fields. Addressing
the incoherent regime, a characteristic minimum emerges in the mean first
passage time to reach an absorbing neighboring state whenever the intrinsic
time scale of the modulation matches the characteristic time scale of the
system dynamics. For the case of deterministic periodic driving, the first
passage time probability density function (pdf) displays a complex,
multi-peaked behavior, which depends crucially on the details of initial phase,
frequency, and strength of the driving. As an interesting feature we find that
the mean first passage time enters the resonant activation regime at a critical
frequency $\nu^*$ which depends very weakly on the strength of the driving.
Moreover, we provide the relation between the first passage time pdf and the
statistics of residence times.
