An Optical Trap for $^{85}$Rb and $^{87}$Rb

We report on the simultaneous optical trapping of an ultra-cold mixture of $^{85}$Rb and $^{87}$Rb. Using this trap we have been able to explore the interspecies Feshbach resonance between $^{85}$Rb and $^{87}$Rb. With adiabatic magnetic field ramps a Feshbach resonance provides the opportunity to create hetronuclear molecules, as well as superpositions of atomic and molecular states. Recently at JILA, the $^{85}$Rb Feshbach resonance has demonstrated that large molecular conversion efficiency and long molecular lifetimes demand atomic gases with low densities [1]. In consideration of this we discuss our efforts in implementing an optical trap with very weak confinement. We acknowledge the funding for this work from the NSF and ONR. [1] E. Hodby\textit{, et al}. cond-mat/0411487