Experimental Study of the BEC-BCS Crossover Region in Lithium 6

We report Bose-Einstein condensation of weakly bound $^{6}\mathrm{L}\mathrm{i}_{2}$ molecules in a crossed optical trap near a Feshbach resonance. We measure a molecule-molecule scattering length of ${170}_{\ensuremath{-}60}^{+100}\text{ }\mathrm{n}\mathrm{m}$ at $770\text{ }\mathrm{G}$, in good agreement with theory. We study the 2D expansion of the cloud and show deviation from hydrodynamic behavior in the BEC-BCS crossover region.

• CN
  Centre National de la Recherche Scientifique