The basic elements of point source interferometry are depicted here. (a) The method starts with a small cloud of ultracold atoms (blue), which is launched upward inside an evacuated enclosure. At the beginning of the trajectory, a laser pulse (red) splits the cloud into two clouds, which both expand as they rise and fall. A second pulse at the top of the trajectory acts as a mirror. (b) When the clouds reach the bottom of the enclosure, a third pulse recombines them. The resulting interference pattern is recorded with two CCD cameras.