Feshbach spectroscopy of a K-Rb atomic mixture

We perform extensive magnetic Feshbach spectroscopy of an ultracold mixture of fermionic K40 and bosonic Rb87 atoms. The magnetic-field locations of 13 interspecies resonances are used to construct a quantum collision model able to predict accurate collisional parameters for all K-Rb isotopic pairs. In particular, we determine the interspecies s-wave singlet and triplet scattering lengths for the K40-Rb87 mixture as (-108±3)a0 and (-205±5)a0, respectively. We also predict accurate scattering lengths and the position of Feshbach resonances for the other K-Rb isotopic pairs. We discuss the consequences of our results for current and future experiments with ultracold K-Rb mixtures.