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arXiv:1709.03796 · Physical Review A

Feshbach spectroscopy and dual-species Bose-Einstein condensation of Na23−K39 mixtures

Torben Schulze, Torsten Hartmann, Kai K. Voges, Matthias W. Gempel, E. Tiemann, Alessandro Zenesini, Silke Ospelkaus

Published Feb 13, 2018• 45 citations
arXivHTMLPDF

Abstract

We present measurements of interspecies Feshbach resonances and subsequent creation of dual-species Bose-Einstein condensates of $^{23}\mathrm{Na}$ and $^{39}\mathrm{K}$. We prepare both optically trapped ensembles in the spin state $\left|f=1,{m}_{f}=\ensuremath{-}1\right\ensuremath{\rangle}$ and perform atom loss spectroscopy in a magnetic field range from $0$ to $700\phantom{\rule{0.16em}{0ex}}\mathrm{G}$. The observed features include several $s$-wave poles and a zero crossing of the interspecies scattering length as well as inelastic two-body contributions in the $\mathcal{M}={m}_{\mathrm{Na}}+{m}_{\mathrm{K}}=\ensuremath{-}2$ submanifold. We identify and discuss the suitability of different magnetic field regions for the purposes of sympathetic cooling of $^{39}\mathrm{K}$ and achieving dual-species degeneracy. Two condensates are created simultaneously by evaporation at a magnetic field of about $150\phantom{\rule{0.16em}{0ex}}\mathrm{G}$, which provides sizable intra- and interspecies scattering rates needed for fast thermalization. The impact of the differential gravitational sag on the miscibility criterion for the mixture is discussed. Our results serve as a promising starting point for the magnetoassociation into quantum degenerate $^{23}\mathrm{Na}^{39}\mathrm{K}$ Feshbach molecules.

DOI
10.1103/physreva.97.023623

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Abstract We have realized a dual-species Bose–Einstein condensate (BEC) of 23 Na and 87 Rb atoms and observed its immiscibility. Because of the favorable background intra- and inter-species scattering lengths, stable condensates can be obtained via efficient evaporative cooling and sympathetic cooling without the need for fine tuning of the interactions. Our system thus provides a clean platform for studying inter-species interactions–driven effects in superfluid mixtures. With a Feshbach resonance, we have successfully created double BECs with largely tunable inter-species interactions and studied the miscible–immiscible phase transition.
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