Observation of the BEC-BCS crossover in a degenerate Fermi gas of lithium atoms

We observe characteristic atomic behaviors in the Bose-Einstein-condensation-Bardeen-Cooper-Schrieffer (BECBCS) crossover, by accurately tuning the magnetic field across the Feshbach resonance of lithium atoms. The magnetic field is calibrated by measuring the Zeeman shift of the optical transition. A non-monotonic anisotropic expansion is observed across the Feshbach resonance. The density distribution is explored in different interacting regimes, where a condensate of diatomic molecules forms in the BEC limit with the indication of a bimodal distribution. We also measure the three-body recombination atom loss in the BEC-BCS crossover, and find that the magnetic field of the maximum atom loss is in the BEC limit and gets closer to the Feshbach resonance when decreasing the atom temperature, which agrees with previous experiments and theoretical prediction. This work builds up a controllable platform for the study on the strongly interacting Fermi gas.

Automated summary

In this study, characteristic atomic behaviors in the BECBCS crossover were observed by tuning the magnetic field across the Feshbach resonance, revealing a non-monotonic anisotropic expansion and indication of bimodal distribution in a condensate of diatomic molecules. The measurement of three-body recombination atom loss also supported previous experiments and theoretical predictions, showing that the maximum atom loss occurs in the BEC limit and gets closer to the Feshbach resonance at lower atom temperatures. This work provides a controllable platform for studying strongly interacting Fermi gases.