COHERENT FREQUENCY-SHIFT OF ATOMIC MATTER WAVES

We demonstrate how Bragg diffraction of atomic matter waves at a time- modulated thick standing light wave can be used to coherently shift th e de Broglie frequency of the diffracted atoms. The coherent frequency shift is experimentally confirmed by interferometric superposition of modulated and unmodulated atoms resulting in time-dependent interfere nce fringes. Our frequency shifter for atomic matter waves is a genera lization of an acousto-optic frequency shifter for photons.