DEMONSTRATION OF A NOVEL ATOMIC-BEAM SPLITTER

We have demonstrated a novel beam splitter for atoms. The J=1 to J=0 system in metastable helium has two independent ''dark'' states which are radiatively stable. By preparing atoms in the two ''dark'' states of the 2(3)S(1) level and passing them through a sequence of partially overlapping laser beams tuned to the 2(3)S(1)-2(3)P(0) transition, we cause the atoms in one ''dark'' state to be deflected by integral multiples of 2hk, while the atoms in the other ''dark'' state are undeflected. The excited 2(3)P(0) state is not populated, so the process is unaffected by spontaneous emission. We have observed up to 90% coherent momentum transfer with 4hk deflection. We conclude by describing how one might construct an atom interferometer based on these ''dark state'' beam splitters.