Feshbach spectroscopy and dual-species Bose-Einstein condensation of Na 23 - K 39 mixtures

We present measurements of interspecies Feshbach resonances and subsequent creation of dual-species Bose-Einstein condensates of Na23 and K39. We prepare both optically trapped ensembles in the spin state f=1,mf=-1 and perform atom loss spectroscopy in a magnetic field range from 0 to 700G. 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 M=mNa+mK=-2 submanifold. We identify and discuss the suitability of different magnetic field regions for the purposes of sympathetic cooling of K39 and achieving dual-species degeneracy. Two condensates are created simultaneously by evaporation at a magnetic field of about 150G, 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 Na23K39 Feshbach molecules.