Observation of spatially localized atomic electron wave packets.

We have excited and detected an atomic electron wave packet that is localized in the polar and azimuthal angles. The wave packet is formed through the coherent superposition of Rydberg states of atomic sodium. The superposition is achieved by short-pulse optical excitation of the atom in the presence of a strong rf field. The wave packet is detected by dc field ionization. The behavior of this wave packet in a strong dc field is much different from that of an eigenstate. This behavior agrees well with a simple classical model.