Observation of a shape resonance in the collision of two coldRb87atoms

Abstract

We observe a shape resonance in the scattering of two ultracold ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$ atoms, causing the colliding atoms to form a long-living compound system inside an l=2 centrifugal barrier. Its existence follows from a photoassociation experiment in a gas sample of doubly polarized ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$ atoms. Using it we are able to carry out direct determinations of the triplet scattering length for ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$, relevant to Bose-Einstein condensation experiments, and of the Rb+Rb ${\mathrm{C}}_6$ dispersion coefficient. Consequences for the ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$ scattering length are discussed.