The dynamics of Rydberg states of atomic hydrogen perturbed simultaneously by a static electric field and a resonant microwave field of elliptical polarization is analyzed in the quantum perturbative limit of small amplitudes. For some configurations, the secular motion (i.e., evolution in time of the elliptical electronic trajectory) may be classically predominantly chaotic. By changing the orientation of the static field with respect to the polarization of the microwave field, one can modify the global symmetries of the system and break any generalized time-reversal invariance. This has a dramatic effect on the statistical properties of the energy levels.

• Received 29 June 1999

DOI:https://doi.org/10.1103/PhysRevLett.83.2922