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

TL;DR

This paper reports the creation of tunable dual-species Bose-Einstein condensates of potassium-39 and rubidium-87, utilizing Feshbach resonances for precise control of interactions, enabling advanced studies in quantum physics and metrology.

Contribution

The study demonstrates the production of dual-species BECs with tunable interactions via Feshbach resonances, including a novel method for precision spectroscopy and control of interspecies scattering.

Findings

Identified a Feshbach resonance at 117.56 G with a width of 1.21 G.

Achieved sympathetic cooling of $^{39}$K with $^{87}$Rb to produce dual-species BECs.

Determined the interspecies background scattering length to be 28.5 a0.

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 $\left| F=1,m_F=-1 \right\rangle$ 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.