Experimental study of Lithium-6 close to Feshbach resonances

We discuss recent experiments performed on ultra-cold gases of fermionic $^6\mathrm{Li}$ in a crossed-beam dipole trap. This system enables the investigation of the so-called BEC-BCS crossover region. Using a Feshbach resonance, the magnitude of the atomic interactions can be tuned between the strongly interacting regime, where the ground state is a Bose-Einstein condensate (BEC) of molecules, to the weakly interacting regime, where the BCS (Bardeen-Cooper-Schrieffer) theory of superconductivity is more appropriate. A broad s-wave resonance was used to form a BEC of weakly bound $^6\mathrm{Li}_2$ molecules in the optical trap. The molecule- molecule scattering length and the expansion energy of the cloud in the crossover region were measured. Furthermore, we have studied the scattering properties of the gas close to several p-wave Feshbach resonances, whose positions are in very good agreement with theory. We have also experimentally shown the existence of new s-wave resonances in the heteronuclear $^6 \mathrm{Li}$-$^7\mathrm{Li}$ mixture.