Measurement of the Low-Energy Rb^+–Rb Total Collision Rate in an Ion-Neutral Hybrid Trap

An ion–neutral hybrid trap is built to study low-energy ion–atom collisions. The ion–neutral hybrid trap is combined with two spatially concentric traps: a linear Paul trap for the ionic species and a magneto-optical trap (MOT) for the neutral species. The total ion–atom collision rate coefficient k_\rm ia between^87Rb atoms and optically dark ^87Rb^+ ions is measured by monitoring the reduction of the steady-state MOT atoms by sequentially introducing various mechanisms, namely photoionization and ion–atom collisions. In contrast to other experiments, a concise experimental procedure is devised to obtain the loss rates of the MOT atoms due to photoionization and ion–atom collisions in one experimental cycle, and then the collision rate k_\rm ia of cold ^87Rb atoms with ^87Rb^+ ions is deduced to 0.94(\pm0.24)\times10^-13 m^3/s with T_\rm i=3770(\pm100) K measured by the time of flight of the ion signal. The measurements show good agreement with the collision rate derived from the Langevin model.