Atom interferometry with degenerate quantum gases in a vertical optical lattice

We study the interference of degenerate quantum gases in a vertical optical lattice and show that an interference pattern can be observed for both Bose and Fermi gases. The latter is observable as soon as the momentum spread of the Fermi gas is reduced below the recoil momentum of the lattice. When the atoms are trapped in the potential, the contrast of the interference patterns evolves differently with time. While the Bose condensate loses its fringe contrast after a few oscillations, the fermions oscillate for many periods without a degradation of the visibility. We attribute this difference to the interaction between the particles, which is absent for the Fermi gas because the Pauli principle forbids collisions between identical fermions at ultralow temperatures. Taking advantage of this property, we employ a degenerate Fermi gas to demonstrate a high-precision interferometric measurement of forces on a microscopic length scale.