Nonclassical states from the joint statistics of simultaneous measurements

Abstract

Nonclassicality cannot be a single-observable property since the statistics of any quantum observable is compatible with classical physics. We develop a general procedure to reveal nonclassical behavior from the joint measurement of multiple observables. This requires enlarged spaces and couplings with auxiliary degrees of freedom so it must be followed by an inversion procedure to infer system properties from the observed statistics. In particular this discloses nonclassical properties of standard examples of classical-like behavior, such as SU(2) and Glauber coherent states. Moreover, when combined with other criteria it would imply that every quantum state would be nonclassical.