SYMPATHETIC COOLING OF FERMIONIC LITHIUM VIA A BOSONIC RUBIDIUM GAS

The Pauli exclusion principle inhibits s-wave collisions between fermionic ⁶Li atoms and renders thermalization and evaporative cooling at low temperatures inefficient. A way around this problem is sympathetic cooling by a different actively cooled atomic species. With this technique, using bosonic ⁸⁷Rb as cooling agent, we obtain a mixture of quantum-degenerate gases, where the Rb cloud is colder than the critical temperature for Bose-Einstein condensation and the Li cloud colder than the Fermi temperature. From measurements of the thermalization velocity we estimate the interspecies s-wave triplet scattering length .