Finite-resolution measurement of the nonclassical polarization statistics of entangled photon pairs

By limiting the resolution of quantum measurements, measurement-induced changes of the quantum state can be reduced, permitting subsequent measurements of variables that do not commute with the initially measured property. It is then possible to determine correlations between noncommuting variables experimentally. The application of this method to the polarization statistics of entangled photon pairs reveals that negative conditional probabilities between nonorthogonal polarization components are responsible for the violation of Bell’s inequalities. Such negative probabilities can also be observed in finite-resolution measurements of the polarization of a single photon. The violation of Bell’s inequalities therefore originates from local properties of the quantum statistics of single-photon polarization.