Spin excitations in a cavity hop coherently over long distances

One of the most counterintuitive aspects of quantum mechanics is its nonlocality: the encoding of information in the correlations between widely separated particles (see, for example, Physics Today, August 2017, page 14). Typical demonstrations of spatially extended entanglement involve pairwise entangled particles produced two by two. But in the spins of atoms coupled to an optical cavity, researchers have also created massively parallel correlations, which can extend over macroscopic distances. Until recently, the dynamics that give rise to those correlations have been inferred only from global measurements, such as the total magnetization of the atomic cloud. Now Monika Schleier-Smith and colleagues at Stanford University are combining nonlocal spin interactions with the capability to locally prepare and detect the atomic spin states.