Coherent scattering with pulsed matter beams

We present a quantum theory for the interaction of a quantum target with a time dependent matter beam. When several pulses in the incident beam arrive with a period tau, transitions between levels with an energy difference h/ tau can be enhanced. Unlike all previous studies, we find that transitions in passive targets can distinguish between an incoherent beam and a beam wi th a coherent wave packet structure. As an example, Lye calculate the trans ition probability of Rb Rydberg atoms interacting with a pulsed electron be am.