85Rb tunable-interaction Bose-Einstein condensate machine

We describe our experimental setup for creating stable Bose-Einstein condensates (BECs) of Rb-85 with tunable interparticle interactions. We use sympathetic cooling with Rb-87 in two stages, initially in a tight Ioffe-Pritchard magnetic trap and subsequently in a weak, large-volume, crossed optical dipole trap, using the 155 G Feshbach resonance to manipulate the elastic and inelastic scattering properties of the Rb-85 atoms. Typical Rb-85 condensates contain 4 x 10(4) atoms with a scattering length of a=+200a(0). Many aspects of the design presented here could be adapted to other dual-species BEC machines, including those involving degenerate Fermi-Bose mixtures. Our minimalist apparatus is well suited to experiments on dual-species and spinor Rb condensates, and has several simplifications over the Rb-85 BEC machine at JILA, which we discuss at the end of this article. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3430538]