OBSERVING THE POSITION SPREAD OF ATOMIC WAVE-PACKETS

We report on a novel method to measure the spatial extension of atomic wave packets confined in the microscopic light traps of a three-dimen sional optical lattice, We compare the powers Bragg scattered by two d ifferent classes of lattice planes from two blue light beams incident on the atomic lattice under different Bragg angles. We have used this technique to explore unusual atomic vibrational modes which display a position spread oscillating at twice the fundamental vibrational frequ ency.