Bragg spectroscopy and Ramsey interferometry with an ultracold Fermi gas

We report on the observation of Bragg scattering of an ultracold Fermi gas of ⁶Li atoms at a dynamic optical potential. The momentum states produced in this way oscillate in the trap for time scales on the order of seconds, nearly unperturbed by collisions, which are absent for ultracold fermions due to the Pauli principle. In contrast, interactions in a mixture with ⁸⁷Rb atoms lead to rapid damping. The coherence of these states is demonstrated by Ramsey-type matter wave interferometry. The signal is improved using an echo pulse sequence, allowing us to observe coherence times longer than 100 μs. Finally, we use Bragg spectroscopy to measure the in-situ momentum distribution of the ⁶Li cloud. Signatures for the degeneracy of the Fermi gas can be observed directly from the momentum distribution of the atoms inside the trap.