We review three recent experiments showing the application of atom interferometers in a variety of areas. We present initial results for the dispersion of the index of refraction for matter-waves. This experiment determines the phase shift in atom-atom scattering where it establishes the existence of glory oscillations in this quantity. The fundamental issue of decoherence in quantum mechanics was probed in a second experiment, a version of Feynman's gedanken experiment in which a single photon was scattered from each atom as it passed through the interferometer. The "which path" information that could in principal be gained by observing the scattered photon is shown to cause a loss of contrast in the atom interference fringes. We show that the lost coherence can be regained by observing interference fringes formed only by those atoms which scatter a photon into a small subset of possible final directions. In the third experiment, we demonstrate the high sensitivity of atom interferometers to inertial effects, showing that our interferometer can measure small rotations with a sensitivity of better than 50 milli-earthrate (0.1 deg per minute) in a one second measurement.

We have scattered single photons from interfering de Broglie waves in an atom interferometer and observed contrast loss and revivals as the separation of the interfering paths at the point of scattering is increased. Additionally, we have demonstrated that the lost coherence can be recovered by observing only atoms that are correlated with photons emitted into a limited angular range.