Condensation of Pairs of Fermionic Atoms near a Feshbach Resonance

Abstract

We have observed Bose-Einstein condensation of pairs of fermionic atoms in an ultracold ${}^6\mathrm{Li}$ gas at magnetic fields above a Feshbach resonance, where no stable ${}^6\mathrm{Li}_2$ molecules would exist in vacuum. We accurately determined the position of the resonance to be $822\pm 3\mathrm{G}$. Molecular Bose-Einstein condensates were detected after a fast magnetic field ramp, which transferred pairs of atoms at close distances into bound molecules. Condensate fractions as high as 80% were obtained. The large condensate fractions are interpreted in terms of preexisting molecules which are quasistable even above the two-body Feshbach resonance due to the presence of the degenerate Fermi gas.