Measurement of positive and negative scattering lengths in a Fermi gas of atoms

• Published in: Physical review letters Vol. 90; no. 23; p. 230404
• Main Authors: Regal, C A, Jin, D S
• Format: Journal Article
• Language: English
• Published: United States 13.06.2003
• ISSN: 0031-9007
• DOI: 10.1103/physrevlett.90.230404

We report on progress toward realizing a predicted superfluid phase in a Fermi gas of atoms. We present measurements of both large positive and large negative scattering lengths in a quantum degenerate Fermi gas of atoms near a magnetic-field Feshbach resonance. We employ an rf spectroscopy technique to directly measure the mean-field interaction energy, which is proportional to the s-wave scattering length. Near the peak of the resonance we observe a saturation of the interaction energy; it is in this strongly interacting regime that superfluidity is predicted to occur. We have also observed anisotropic expansion of the gas, which has recently been suggested as a signature of superfluidity. However, we find that this can be attributed to a purely collisional effect.