Wave Packets in Perturbed Rydberg Systems

We have excited wave packets in perturbed Rydberg states of barium, an atom with two optically active electrons, and have observed qualitatively different wave packets from those seen in one-electron atoms. In particular, we have found that electron-electron scattering quickly leads to excitation of a doubly excited state and subsequent passage of the population back and forth between different configurations or channels, the quantum analog of two coupled pendula. The experimental results can be successfully described by quantum defect theory.