Time-independent and time-dependent photoassociation of spin-polarized rubidium

We extract information about collisions of ultra-cold ground-state rubidium atoms from observations of a g-wave shape resonance in the 85Rb + 85Rb system via time-independent and time-dependent photoassociation. The shape resonance arises from a quasi-bound state inside a centrifugal barrier that enhances the excitation to the bound electronically excited state by the photoassociation laser in the time-independent experiment. The shape resonance is sufficiently long-lived that its build-up through the barrier can be observed by first depleting it via a photoassociation laser pulse and then measuring the rate of photoassociation by a second laser pulse with a variable delay time. A combined method of analysis of the time-independent and time-dependent experiments is presented. We discuss the spectroscopy of states of two particles with spin trapped inside a centrifugal barrier, interacting via direct and indirect spin-spin interactions