Experimental characterization of Gaussian quantum discord generated by   four-wave mixing
  We experimentally determine the 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 discord, 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 quantum discord may exhibit sub- or superadditivity depending on which spatial channels are selected. 
Ulrich Vogl, Ryan T. Glasser, Quentin Glorieux, Jeremy B. Clark, Neil   Corzo-Trejo, and Paul D. Lett
quant-ph