Exponential and nonexponential localization of the one-dimensional periodically kicked Rydberg atom - art. no. 023408

We investigate the quantum localization of the one-dimensional Rydberg atom subject to a unidirectional periodic train of impulses. For high frequenci es of the train the classical system becomes chaotic and leads to fast ioni zation. By contrast, the quantum system is found to be remarkably stable. W e identify for this system the coexistence of different localization mechan isms associated with resonant and nonresonant diffusion. We find for the su ppression of nonresonant diffusion an exponential localization whose locali zation length can be related to the classical dynamics in terms of the "sca rs" of the unstable periodic orbits. We show that the localization length i s determined by the energy excursion along the periodic orbits. The suppres sion of resonant diffusion along the sequence of photonic peaks is found to be nonexponential due to the presence of high harmonics in the driving for ce.