Coherent and incoherent chaotic tunneling near singlet-doublet crossings

In the spectrum of systems showing chaos-assisted tunneling, three-state cr ossings are formed when a chaotic singlet intersects a tunnel doublet. We s tudy the dissipative quantum dynamics in the vicinity of such crossings. A harmonically driven double well coupled to a bath serves as a model. Markov and rotating-wave approximations are introduced with respect to the Floque t spectrum of the time-dependent central system. The resulting master equat ion is integrated numerically. We find various types of transient tunneling , determined by the relation of the level width to the inherent energy scal es of the crossing. The decay of coherent tunneling can be significantly re tarded or accelerated. Modifications of the quantum asymptotic state by the crossing are also studied. The comparison with a simple three-state model shows that in contrast to the undamped case, the participation of states ou tside the crossing cannot be neglected in the presence of dissipation. [S10 63-651X(98)05212-X].