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.
@article{arxiv.0709.3437,
title = {Azimuthal distinguishability of entangled photons generated in spontaneous parametric down-conversion},
author = {Clara I. Osorio and Gabriel Molina-Terriza and Blanca G. Font and Juan P. Torres},
journal= {arXiv preprint arXiv:0709.3437},
year = {2009}
}