Ketterle presents plenary talk at the American Physical Society March meeting

Wolfgang Ketterle (Massachusetts Institute of Technology) was invited to talk to a plenary session of the APS March meeting in Montreal. He reported that his group has observed Bose-Einstein condensation of molecules. When a spin mixture of fermionic Li atoms was evaporatively cooled in an optical dipole trap near a Feshbach resonance, the atomic gas was converted into Li2 molecules. On cooling below the temperature of 600 nK, a Bose-Einstein condensate of up to 900,000 molecules was identified by the sudden onset of a bimodal density distribution. This condensate realizes the limit of tightly-bound fermion pairs in the crossover between BCS superfluidity and Bose-Einstein condensation.

A paper on this topic was published recently in Physics Review Letters (M.W. Zwierlein, C.A. Stan, C.H. Schunck, S.M.F. Raupach, A.J. Kerman, and W. Ketterle: Condensation of Pairs of Fermionic Atoms Near a Feshbach Resonance, Phys. Rev. Lett. 92, 120403 (2004)). The paper reports that they have observed Bose-Einstein condensation of pairs of fermionic atoms in an ultracold 6Li gas at magnetic fields above a Feshbach resonance, where no stable 6Li2 molecules would exist in vacuum. They accurately determined the position of the resonance to be 822±3 Gauss. 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.