Breaking time reversal symmetry in chaotic driven Rydberg atoms

We consider the dynamics of Rydberg states of the hydrogen atom driven by a microwave field of elliptical polarization, with a possible additional static electric field. We concentrate on the effect of a resonant weak field-whose frequency is close to the Kepler frequency of the electron around the nucleus-which essentially produces no ionization of the atom, but completely mixes the various states inside an hydrogenic manifold of fixed principal quantum number. For sufficiently small fields, a perturbative approach (both in classical and quantum mechanics) is relevant. For some configurations of the fields, the classical secular motion (i.e., evolution in time of the elliptical electronic trajectory) is shown to be predominantly chaotic. Changing the orientation of the static field with respect to the polarization of the microwave field allows us to investigate the effect of generalized time-reversal symmetry breaking on the statistical properties of energy levels. (C) 2000 Academic Press.