Dissipative dynamics in a quantum bistable system: Crossover from weak   to strong damping
  The dissipative dynamics of a quantum bistable system coupled to a Ohmic heat bath is investigated beyond the spin-boson approximation. Within the path-integral approach to quantum dissipation, we propose an approximation scheme which exploits the separation of time scales between intra- and interwell (tunneling) dynamics. The resulting generalized master equation for the populations in a space localized basis enables us to investigate a wide range of temperatures and system-environment coupling strengths. A phase diagram in the coupling-temperature space is provided to give a comprehensive account of the different dynamical regimes. 
Luca Magazz\`u, Davide Valenti, Bernardo Spagnolo, Milena Grifoni
cond-mat.stat-mech