In Situ Momentum Distribution Measurement of a Quantum Degenerate Fermi Gas using Raman Spectroscopy

TL;DR

This paper demonstrates a novel Raman spectroscopy method to directly measure the momentum distribution of a quantum degenerate Fermi gas in a trap, providing accurate temperature measurements and spatial selectivity.

Contribution

The authors introduce a Raman spectroscopy technique for in situ momentum distribution measurement of trapped Fermi gases, enabling spatially selective and rapid analysis.

Findings

Measured momentum distributions match theoretical predictions.

Extracted temperatures agree with traditional time-of-flight results.

Technique is sensitive, fast, and applicable to small atomic clouds.

Abstract

The ability to directly measure the momentum distribution of quantum gases is both unique to these systems and pivotal in extracting many other important observables. Here we use Raman transitions to measure the momentum distribution of a weakly-interacting Fermi gas in a harmonic trap. For narrow atomic dispersions, momentum and energy conservation imply a linear relation between the two-photon detuning and the atomic momentum. We detect the number of atoms transferred by the Raman beams using sensitive fluorescence detection in a magneto-optical trap. We employ this technique to a degenerate weakly-interacting Fermi gas at different temperatures. The measured momentum distributions match theoretical curves over two decades, and the extracted temperatures are in very good agreement with the ones obtained from a conventional time-of-flight technique. The main advantages of our measurement scheme are that it can be spatially selective and applied to a trapped gas, it can be completed in a relatively short time, and due to its high sensitivity, it can be used with very small clouds.