  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.
