Fig. 2From: Sympathetic cooling of molecular ions with ultracold atomsSample trajectories showing the effect of a collision at t=0 that reduces the trapped particle velocity to zero in a a static and b rf Paul trap. In the static case, a stopping collision always leads to cooling (i.e. reduced amplitude of the oscillation), however, in the time-dependent potential of the Paul trap a stopping collision can lead to heatingBack to article page