DYNAMICS OF THE DISSIPATIVE 2-STATE SYSTEM UNDER AC MODULATION OF BIAS AND COUPLING ENERGY

We consider a driven dissipative two-state system subject to periodic modulation of both of its two parameters. The exact master equation th at governs the dynamics is derived. Closed form analytical solutions a re presented within the noninteracting-blip approximation for the stoc hastic forces, and for the exactly solvable case alpha=1/2 of the Ohmi c viscosity. We apply these results to a tight-binding particle with z ero intrinsic bias. Selection rules are obeyed for arbitrary dissipati on. For Ohmic dissipation, the effects of fast asymmetry modulation re sult in an overall reduction of quantum coherence and in a possible lo calization. On the contrary,a multiplicative modulation of the tunnell ing coupling leads to an exponential enhancement of tunnelling.