The dynamics of Rydberg states of atomic hydrogen driven by elliptically polarized microwaves of frequency fulfilling the 2:1 classical resonance condition is investigated both semiclassically and quantum mechanically in a simplified two-dimensional model of an atom. Semiclassical results for quasienergies of the system are shown to be in good agreement with exact quantum data. The structures of the quantum states are found to reflect the underlying classical dynamics; especially we show the existence of nonspreading wave packets propagating on elliptical trajectories.

• Received 17 September 1998

DOI:https://doi.org/10.1103/PhysRevA.59.1707