Quantum mechanical manifestation of cantori: Wave-packet localization in stochastic regions

Numerical calculations for a model anharmonic system interacting with a laser are used to analyze the quantum mechanical implications of classical structure in stochastic regions due to cantori (associated with the breakup of invariant Kolmogorov-Arnol'd-Moser surfaces). The numerical results show that a quantum wave packet may remain localized, even though classical orbits are strongly chaotic. Consequently, the quantum dynamics continues to exhibit ``tunnelinglike'' behavior even when diffusion is not classically forbidden.