In what is arguably the first manifestation of gravity in a quantum-mechanical system, physicists have observed the tidal phase shift in an atom interferometer. Peter Asenbaum of Stanford University and colleagues used a dual light-pulse rubidium atom interferometer, in which a macroscopic spatial superposition state acts as a nonlocal probe of space–time. Space–time curvature induces tidal forces on the wave function of a single quantum system, and the team was able to measure a phase shift associated with such tidal forces. Additionally, the dual atom interferometer works as a gradiometer for precise gravitational measurements and could be used for measurements of the gravitational constant or the gravitational Aharonov–Bohm effect.