Chaotic ionization of a highly excited hydrogen atom in parallel electric and magnetic fields

We present results of our simulations of the ionization of a hydrogen atom excited to a Rydberg wave packet in the presence of external parallel electric and magnetic fields. This is an example of an open, quantum system whose classical counterpart has been shown to display chaos in the time domain. Within the framework of classical mechanics, electrons escape through chaos induced pulse trains. We reproduce such previously observed signatures of classical chaos in the time-dependent current of ionizing electrons and study the interference effects between the outgoing pulse trains which is absent in the classical picture. Our attempts at manipulating the ionization pulse trains and the effect of core scattering coupled with the chaotic ionization are also discussed. We further investigate the onset of chaos as a function of the scaled energy of the system. We find that for relatively high magnetic fields, quantum-mechanical ionization current shows erratic fluctuations in contrast with the classical current which shows transition to regularity. We conclude that the oscillations result from the decrease in the number of the ionization channels for the higher magnetic field strengths. We further study the timedependent autocorrelation function and its Fourier transform to look for the effects of the Landau quantization in the photoabsorption spectrum. Our results include calculations via the classical trajectory Monte Carlo method to compare our non-perturbative quantum-mechanical results with the underlying chaotic classical dynamics. (Some figures in this article are in colour only in the electronic version)