Bragg spectroscopy and Ramsey interferometry with an ultracold Fermi gas

TL;DR

This paper demonstrates Bragg scattering and Ramsey interferometry with an ultracold Fermi gas of 6Li, revealing long-lived momentum states, coherence properties, and direct measurement of the Fermi gas's momentum distribution.

Contribution

It introduces the first combined use of Bragg spectroscopy and Ramsey interferometry on an ultracold Fermi gas, highlighting long coherence times and direct momentum distribution measurement.

Findings

Long-lived oscillations of momentum states in the trap.

Coherence times exceeding 100 microseconds with echo sequences.

Direct observation of Fermi degeneracy from momentum distribution.

Abstract

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 mus. 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.