Quantum Chaos on Display

In most systems encountered in our everyday life, small changes in the initial conditions can lead to widely diverging outcomes. Think, for example, of the drawing of lottery numbers. Even if great care was taken in the initial positioning of the balls, and the lottery machine was set in an almost identical rotation, we could hardly expect the same outcome at every draw. Although governed by deterministic laws, such a system is unpredictable. In classical physics, the phenomenon of extreme sensitivity to initial conditions is what defines chaos. Since classical mechanics is only an approximation of the more fundamental theory of quantum mechanics, one may expect to see analogous behavior in the quantum world. However, the laws of quantum mechanics do not permit a similar definition, since they do not lead to exponential sensitivity to the initial conditions. So how does classical chaos emerge from a quantum system? Are there any signatures of chaos in a quantum system whose classical counterpart is chaotic? In Physical Review A, Jonas Larson at Stockholm University, Sweden, and colleagues [1] propose that such questions—at the heart of the research field known as quantum chaos [2, 3]—could be addressed experimentally in an ideal model system: an ultracold atomic gas in which an artificial spin-orbit (SO) coupling is induced by laser fields.