Collisional Properties of Ultracold K-Rb Mixtures

Abstract

We determine the interspecies $s$-wave triplet scattering length ${a}_{3}$ for all K-Rb isotopic mixtures by measuring the elastic cross section for collisions between $^{\mathrm{41}}\mathrm{K}$ and $^{87}\mathrm{R}\mathrm{b}$ in different temperature regimes. The positive value ${a}_{3}=+{163}_{\ensuremath{-}12}^{+57}{a}_{0}$ ensures the stability against collapse of binary $^{41}\mathrm{K}\ensuremath{-}^{87}\mathrm{R}\mathrm{b}$ Bose-Einstein condensates. For the fermion-boson mixture $^{40}\mathrm{K}\ensuremath{-}^{87}\mathrm{R}\mathrm{b}$, we obtain a large and negative scattering length which implies an efficient sympathetic cooling of the fermionic species down to the degenerate regime.