Tunable dual-species Bose-Einstein condensates of ${}^{39}$K and ${}^{87}$Rb

Abstract

We present the production of dual-species Bose-Einstein condensates of ${}^{39}\mathrm{K}$ and ${}^{87}\mathrm{Rb}$. Preparation of both species in the $|F=1,m_F=-1⟩$ 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 $28.5a_0$ 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.

9 pages, 9 figures