Observation of a shape resonance in cold-atom scattering by pulsed photoassociation

We observe the time dependence of a cold-atom collision in a pulsed photoassociation experiment. For a g-wave shape resonance in the Rb-85+Rb-85 system we measure the time needed to build up the resonant state by tunneling through the centrifugal barrier. Combining this with time-independent Rb-85 and Rb-87 photoassociation we determine the resonance energy and find evidence for the decay of the shape resonance into inelastic channels. We also determine the Rb-85+Rb-85+ C-6 coefficient and triplet scattering lengths without relying on ab initio calculations.