Numerical studies of tunneling in a nonharmonic time-dependent potential.

Tunneling through time-dependent potentials is of relevance to a number of physical problems. Using a WKB analysis Azbel' has recently studied the effects of a nonharmonic time-dependent perturbation embedded in an opaque potential barrier. He suggests the existence of three different regimes for transmission in such systems: direct tunneling, activation assisted tunneling, and elevator resonant activation. We address the same problem with a numerical technique based on wave-packet simulations. Our numerical results are in qualitative agreement with Azbel's picture. The outcome depends on the characteristic time T of the nonharmonic potential. There is a transition from direct tunneling to the activation regime around a " crossover " value T c which is determined by the Büttiker-Landauer time, the distance between the initial energy and the lowest resonant level, and the amplitude of the time-dependent perturbation. The total transmission probability is strongly enhanced when entering the activation regime.