VIEWPOINT Seeing Scrambled Spins

P hysicists have long wondered whether and how isolated quantum systems thermalize—questions that are relevant to systems as diverse as ultracold atomic gases and black holes. Recent theoretical and experimental advances are bringing fresh insight into this line of inquiry. At one extreme, researchers have shown that disorder can fully arrest thermalization in certain isolated many-body quantum systems [1]. At the other extreme, surprising results from the field of quantum gravity have established that black holes are, in some sense, the fastest thermalizers in nature [2–4]. A common thread running through these developments is an emerging focus on the dynamics of quantum information, in which thermalization is associated with “scrambling,” or the loss of accessible information. Two groups, one in China [5] and one in the US [6], have taken a step towards tracking this scrambling of information in systems of quantum spins.