Observation of Feshbach resonances between two different atomic species

We have observed three Feshbach resonances in collisions between lithium-6 and sodium-23 atoms. The resonances were identified as narrow loss features when the magnetic field was varied. The molecular states causing these resonances have been identified, and additional lithium-sodium resonances are predicted. These resonances will allow the study of degenerate Bose-Fermi mixtures with adjustable interactions, and could be used to generate ultracold heteronuclear molecules

Formation Time of a Fermion Pair Condensate

The formation time of a condensate of fermionic atom pairs close to a Feshbach resonance was studied. This was done using a phase-shift method in which the delayed response of the many-body system to a modulation of the interaction strength was recorded. The observable was the fraction of condensed molecules in the cloud after a rapid magnetic field ramp across the Feshbach resonance. The measured response time was slow compared to the rapid ramp, which provides final proof that the molecular condensates reflect the presence of fermion pair condensates before the ramp.Comment: 5 pages, 4 figure

Observation of Bose-Einstein Condensation of Molecules

We have observed Bose-Einstein condensation of molecules. When a spin mixture of fermionic Li-6 atoms was evaporatively cooled in an optical dipole trap near a Feshbach resonance, the atomic gas was converted into Li_2 molecules. Below 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.Comment: 4 pages, 3 figure

Condensation of Pairs of Fermionic Atoms Near a Feshbach Resonance

We 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 ^6Li_2 molecules would exist in vacuum. We accurately determined the position of the resonance to be 822+-3 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 pre-existing molecules which are quasi-stable even above the two-body Feshbach resonance due to the presence of the degenerate Fermi gas.Comment: submitted to PRL. v3: clarifying revisions, added referenc

Feshbach Resonances in Fermionic Lithium-6

Feshbach resonances in lithium-6 were experimentally studied and theoretically analyzed. In addition to two previously known s-wave resonances, we found three p-wave resonances. Four of these resonances are narrow and yield a precise value of the singlet scattering length, but do not allow us to accurately predict the location of the broad resonance near 83 mT. Its position was previously measured in a molecule-dissociation experiment for which we, here, discuss systematic shifts

Diatomic molecules in ultracold Fermi gases - Novel composite bosons

We give a brief overview of recent studies of weakly bound homonuclear molecules in ultracold two-component Fermi gases. It is emphasized that they represent novel composite bosons, which exhibit features of Fermi statistics at short intermolecular distances. In particular, Pauli exclusion principle for identical fermionic atoms provides a strong suppression of collisional relaxation of such molecules into deep bound states. We then analyze heteronuclear molecules which are expected to be formed in mixtures of different fermionic atoms. It is found how an increase in the mass ratio for the constituent atoms changes the physics of collisional stability of such molecules compared to the case of homonuclear ones. We discuss Bose-Einstein condensation of these composite bosons and draw prospects for future studies.Comment: 10 pages, 5 figure