VIEWPOINT Measuring the Tidal Force on a

A tom interferometers have been used to make highprecision measurements in a diverse array of fields. Their more familiar optical counterparts, light interferometers, use matter elements such as mirrors and beam splitters to manipulate light waves. Atom interferometers invert these roles: laser pulses manipulate matter waves of atoms. These pulses split a matter wave into two, redirect the two resulting waves along different paths, and later recombine them to produce an interference pattern from which the measurements can be made. Now, Mark Kasevich from Stanford University, California, and colleagues [1] have used an atom interferometer to measure the effect of the tidal force—which is closely related to the curvature of spacetime and thereby to the fundamental description of gravity in general relativity—on an individual particle’s matter wave, or wave function.