Quantum localization in the high-frequency limit

The quantum localization of the periodically kicked Rydberg atom in the limit of high frequencies ν is studied. We show that the quantum suppression of fast chaotic ionization as predicted by classical dynamics persists as ν→∞. Properties of localization in the regime of strong coupling to the continuum due to one-photon transitions are discussed. For the unidirectionally kicked atom, the high-frequency limit of localization is determined by the zero-frequency Stark Hamiltonian. The persistence of quantum localization due to interference of classical trajectories can be understood in terms of smearing out of the instabilities at finite (ℎ/2π). Unstable trajectories whose action differs from each other and from Stark orbits in less than (ℎ/2π) contribute to quantum localization rather than to chaotic ionization