Experimental investigation of initial system-environment correlations   via trace distance evolution
  The trace distance between two states of an open quantum system quantifies their distinguishability, and for a fixed environmental state can increase above its initial value only in the presence of initial system-environment correlations. We provide for the first time experimental evidence of such a behavior. In our all-optical apparatus we exploit spontaneous parametric down conversion as a source of polarization entangled states, and a spatial light modulator to introduce in a general fashion correlations between the polarization and the momentum degrees of freedom, which act as environment. 
Andrea Smirne, Davide Brivio, Simone Cialdi, Bassano Vacchini, Matteo   G. A. Paris
quant-ph