A. Casado, S. Guerra, J. Plácido
We apply the Wigner function formalism to the study of two-photon polarization-momentum hyperentanglement generated in parametric down conversion. It is shown that the consideration of a higher number of degrees of freedom is directly related to the extraction of additional uncorrelated sets of zeropoint modes at the source. We present a general expression for the description of the quantum correlations corresponding to the sixteen Bell-like states, in terms of four beams whose amplitudes are correlated through the stochastic properties of the zeropoint field. Experiments on complete Bellstate measurement and quantum dense coding are analyzed, emphasizing the role of the vacuum field: it carries the quantum information which is extracted at the source, and also introduces some fundamental noise at the idle channels of the analyzers. These two features of the zeropoint field are a common denominator in optical experiments on quantum information.
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http://arxiv.org/abs/1207.5013
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