Quantum versus classical polarization states: When multipoles count

We advocate a simple multipole expansion of the polarization density matrix. The resulting multipoles are used to construct bona fide quasiprobability distributions that appear as a sum of successive moments of the Stokes variables, the first one corresponding to the classical picture on the Poincaré sphere. We employ the particular case of the Q function to formulate a whole hierarchy of measures that properly assess higher-order polarization correlations. © 2013 IOP Publishing Ltd