We investigate the spatio-temporal structure of the bi-photon entanglement in parametric down-conversion (PDC) and we demonstrate its non-factorable X-shaped geometry. Such a structure gives access to the ultra-broad bandwidth of PDC, and can be exploited to achieve a bi-photon temporal localization in the femtosecond range. This extreme localization is connected to our ability to resolve the photon positions in the source near-field. The non factorability opens the possibility of tailoring the temporal entanglement by acting on the spatial degrees of freedom of twin photons.
@article{arxiv.0812.3533,
title = {X-entanglement of PDC photon pairs},
author = {E. Brambilla and L. Caspani and O. Jedrkiewicz and L. A. Lugiato and A. Gatti},
journal= {arXiv preprint arXiv:0812.3533},
year = {2008}
}