  Coherent molecular optics is performed using two-photon Bragg scattering.
Molecules were produced by sweeping an atomic Bose-Einstein condensate through
a Feshbach resonance. The spectral width of the molecular Bragg resonance
corresponded to an instantaneous temperature of 20 nK, indicating that atomic
coherence was transferred directly to the molecules. An autocorrelating
interference technique was used to observe the quadratic spatial dependence of
the phase of an expanding molecular cloud. Finally, atoms initially prepared in
two momentum states were observed to cross-pair with one another, forming
molecules in a third momentum state. This process is analogous to sum-frequency
generation in optics.
