Spin-orbit hybrid entanglement of photons and quantum contextuality

Abstract

We demonstrate electromagnetic quantum states of single photons and of correlated photon pairs exhibiting ``hybrid'' entanglement between spin and orbital angular momentum. These states are obtained from entangled photon pairs emitted by spontaneous parametric down conversion by employing a $q$ plate for coupling the spin and orbital degrees of freedom of a photon. Entanglement and contextual quantum behavior (that is also nonlocal, in the case of photon pairs) is demonstrated by the reported violation of the Clauser-Horne-Shimony-Holt inequality. In addition, a classical analog of the hybrid spin-orbit photonic entanglement is reported and discussed.