Feshbach spectroscopy and dual-species Bose-Einstein condensation of ${}^{23}\mathrm{N}\mathrm{a}-$${}^{39}\mathrm{K}$ mixtures

We present measurements of interspecies Feshbach resonances and subsequent creation of dual-species Bose-Einstein condensates of ${}^{23}\mathrm{N}\mathrm{a}$ and ${}^{39}\mathrm{K}$. We prepare both optically trapped ensembles in the spin state $\mid f=1,m_f=-1⟩$ and perform atom loss spectroscopy in a magnetic field range from 0 to $700\mathrm{G}$. 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 $$\mathcal{M}$ = m_{$\mathrm{N}\mathrm{a}$}+m_{$\mathrm{K}$} = -2$ submanifold. We identify and discuss the suitability of different magnetic field regions for the purposes of sympathetic cooling of \K and achieving dual-species degeneracy. Two condensates are created simultaneously by evaporation at a magnetic field of about $150 , $\mathrm{G}$$, 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 ${}^{23}{\mathrm{N}\mathrm{a}}^{39}\mathrm{K}$ Feshbach molecules.