Observation of temporal behavior of an atomic wave packet localized in an optical potential.

We have investigated the dynamic temporal behavior of atomic motion in a periodic optical potential by detecting a recoil-induced resonance signal. In the slowly moving optical potential, damped oscillations are observed in the transient signal and the oscillation frequency is found to be independent of the moving speed of the potential. By using a Monte Carlo wave-function method, the signal can be attributed to the oscillatory motion of atomic wave packet localized in the potential, where the oscillation frequency corresponds to the energy separation between vibrational levels.