  We experimentally demonstrate that paired photons generated in different
sections of a down-conversion cone, when some of the interacting waves show
Poynting vector walk-off, carry different spatial correlations, and therefore a
different degree of spatial entanglement. This is shown to be in agreement with
theoretical results. We also discuss how this azimuthal distinguishing
information of the down-conversion cone is relevant for the implementation of
quantum sources aimed at the generation of entanglement in other degrees of
freedom, such as polarization.
