A generalized molecule approach capturing the Feshbach-induced pairing physics in the BEC-BCS crossover.

By including the effect of a trap with characteristic energy given by the Fermi temperaturein a two-body two-channel model for Feshbach resonances, we reproduce the measured binding energy of ultracold molecules in aK atomic Fermi gas. We also reproduce the experimental closed-channel fractionacross the BEC-BCS crossover and into the BCS regime of aLi atomic Fermi gas. We obtain the expected behaviorZ∝TFat unitarity, together with the recently measured proportionality constant. Our results are also in agreement with recent measurements of thedependency onon the BCS side, where a significant quantitative discrepancy between experimental data and theory's predictions has been repeatedly reported. In order to contrast with future experiments we report the proportionality constant at unitarity betweenandTFpredicted by our model for aK atomic Fermi gas.