Observation of Resonance Condensation of Fermionic Atom Pairs

We have observed condensation of fermionic atom pairs in the BCS-BEC crossover regime. A trapped gas of fermionic ⁴⁰K atoms is evaporatively cooled to quantum degeneracy and then a magnetic-field Feshbach resonance is used to control the atom-atom interactions. The location of this resonance is precisely determined from low-density measurements of molecule dissociation. In order to search for condensation on either side of the resonance, we introduce a technique that pairwise projects fermionic atoms onto molecules; this enables us to measure the momentum distribution of fermionic atom pairs. The transition to condensation of fermionic atom pairs is mapped out as a function of the initial atom gas temperature T compared to the Fermi temperature T_F for magnetic-field detunings on both the BCS and BEC sides of the resonance.