Electromagnetic Trapping and Cooling of ^7Li

Laser-cooling and atom trapping techniques have led to the realization of Bose-condensed alkalis, including ^7Li, which have increased our understanding of ultracold interactions and macroscopic coherence in matter. As a complement to our experiments with ^7Li, we are working to produce a degenerate gas of fermionic ^6Li with the goal of observing a BCS phase transition in a two-state mixture of ^6Li. In order to circumvent problems associated with evaporatively cooling a fermion, we will trap both isotopes in an electromagnetic trap and sympathetically cool the ^6Li with ^7Li. We are currently working on evaporatively cooling ^7Li, starting with N = 10^9 atoms and T = 700 μ K. These conditions should be sufficient to achieve run-away evaporation. Previous experiments with the (f,m_f) = (2,2) stretched state of ^7Li have shown that the negative triplet scattering length of -27 Bohr drastically limits the number of atoms obtained in the condensate. In contrast to these studies, we should be able to trap the (1,-1) state which scattering calculations have shown to have a positive scattering length of 5 Bohr. A ^7Li condensate in this state would be stable against density fluctuations and have no upper bound to condensate number. By driving atoms from this state back to the stretched state, a direct observation of mean-field induced collapse could be made. Our progress towards achieving these goals will be discussed.