Resonant dynamics of the H atom in an elliptically polarized microwave field

The dynamics of Rydberg states of atomic hydrogen driven by elliptically po larized microwaves of frequency fulfilling the 2:1 classical resonance cond ition is investigated both semiclassically and quantum mechanically in a si mplified two-dimensional model of an atom. Semiclassical results for quasie nergies 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 underly ing classical dynamics; especially we show the existence of nonspreading wa ve packets propagating on elliptical trajectories. [S1050-2947(99)06902-4].