We present the production of dual-species Bose-Einstein condensates of $^{ 39}\mathrm{ K}$ and $^{ 87}\mathrm{ Rb}$. Preparation of both species in the $\left| F=1,m_F=-1 \right\rangle$ state enabled us to exploit a total of three Fesh\-bach resonances which allows for simultaneous Feshbach tuning of the $^{ 39}\mathrm{ K}$ intraspecies and the $^{ 39}\mathrm{ K}$-$^{ 87}\mathrm{ Rb}$ interspecies scattering length. Thus dual-species Bose-Einstein condensates were produced by sympathetic cooling of $^{ 39}\mathrm{ K}$ with $^{ 87}\mathrm{ Rb}$. A dark spontaneous force optical trap was used for $^{ 87}\mathrm{ Rb}$, to reduce the losses in $^{ 39}\mathrm{ K}$ due to light-assisted collisions in the optical trapping phase, which can be of benefit for other dual-species experiments. The tunability of the scattering length was used to perform precision spectroscopy of the interspecies Feshbach resonance located at $117.56(2)\,\mathrm{ G}$ and to determine the width of the resonance to $1.21(5)\,\mathrm{ G}$ by rethermalization measurements. The transition region from miscible to immiscible dual-species condensates was investigated and the interspecies background scattering length was determined to $28.5\,a_\mathrm{ 0}$ using an empirical model. This paves the way for dual-species experiments with $^{ 39}\mathrm{ K}$ and $^{ 87}\mathrm{ Rb}$ BECs ranging from molecular physics to precision metrology.
Categories: cond-mat.quant-gas physics.atom-ph