Experimental characterization of Gaussian quantum discord generated by four-wave mixing

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We experimentally determine the Gaussian quantum discord present in two-mode squeezed vacuum generated by a four-wave mixing process in hot rubidium vapor. The frequency spectra of the discord as well as the quantum and classical mutual information are also measured. In addition, the effects of symmetric attenuation introduced into both modes of the squeezed vacuum on the Gaussian quantum discord, and the quantum mutual information and the classical correlations are examined experimentally. Finally, we show that due to the multi-spatial-mode nature of the four-wave mixing process, the Gaussian quantum discord may exhibit sub- or superadditivity depending on which spatial channels are selected.