IONIZATION VIA CHAOS ASSISTED TUNNELING

A simple example of quantum transport in a classically chaotic system is studied. It consists in a single state lying on a regular island (a stable primary resonance island) that may tunnel into a chaotic sea a nd further escape to infinity via chaotic diffusion. The specific syst em is realistic: It is the hydrogen atom exposed to either linearly or circularly polarized microwaves. We show that the combination of tunn eling followed by chaotic diffusion leads to peculiar statistical fluc tuation properties of the energy and the ionization rate, especially t o enhanced fluctuations compared to the purely chaotic case. An approp riate random matrix model, whose predictions are analytically derived, describes accurately these statistical properties. [S1063-651X(98)023 01-0].