Quantum degenerate Bose-Fermi mixture of chemically different atomic species with widely tunable interactions

Abstract

We have created a quantum degenerate Bose-Fermi mixture of ${}^{23}$Na and ${}^{40}$K with widely tunable interactions via broad interspecies Feshbach resonances. Over 30 Feshbach resonances between ${}^{23}$Na and ${}^{40}$K were identified, including $p$-wave multiplet resonances. The large and negative triplet background scattering length between ${}^{23}$Na and ${}^{40}$K causes a sharp enhancement of the fermion density in the presence of a Bose condensate. As explained via the asymptotic bound-state model, this strong background scattering leads to wide Feshbach resonances observed at low magnetic fields. Our work opens up the prospect to create chemically stable, fermionic ground-state molecules of ${}^{23}$Na-${}^{40}$K, where strong, long-range dipolar interactions would set the dominant energy scale.