Spatial antibunching of photons with parametric down-conversion

The theoretical framework behind a recent experiment by Nogueira et al. [Phys. Rev. Lett. 86, 4009 (2001)] of spatial antibunching in a two-photon state generated by collinear type-II parametric down-conversion and a birefringent double slit is presented. The fourth-order quantum correlation function is evaluated and shown to violate the classical Schwarz-type inequality, ensuring that the field does not have a classical analog. We expect these results to be useful in the rapidly growing fields of quantum imaging and quantum information.