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We have excited and detected a radially localized electronic wavepacket in atomic rubidium. The wavepacket is formed of an optically induced coherent superposition of Rydberg states with mean principal quantum number, n = 62. The motion ofthe wavepacket on a classical trajectory is monitored in a time-delayed ionization experiment. The collapse and revival of the classical dynamics is observed. During the period of non-classical behaviour we observe, for the first time, a partial revival of the wavepacket.

We describe our use of recoil-induced resonances or stimulated optical Compton scattering to measure the velocity distribution of laser-cooled cesium atoms in one dimension. The technique works well at velocities near 1 cm/s, is insensitive to the effects of light shifts or stray fields, requires only a few mm of work space, and may be completed in 1 ms. It may be extended to allow the measurement of velocity distributions in three dimensions and for in situ measurements in optical molasses, traps, or lattices. Our measurements are compared with traditional ballistic measurements in the same apparatus.PACS number(s): 32.80. Pj, 42.50.Vk