Engineering of two-photon spatial quantum correlations behind a double slit

This paper demonstrates the engineering of spatially entangled two-photon states behind a double slit by tailoring the incident pure two-photon state. We experimentally characterize many different two-photon states by measuring their complete two-photon interference patterns in the far field of the double slit. Spatial entanglement right behind the double slit can reside in either the modulus or the phase of the two-photon field. The balance between these two types of entanglement is fully controlled by experimentally utilizing the phase-front curvatures of the pump beam and the phase-matching profile. We project either a far-field image or a magnified near-field image of the two-photon source onto the double slit. Our theoretical analysis shows how the two-photon interference pattern behind the double slit effectively acts as a phase-sensitive probe of the incident two-photon field profile. We thus present phase-sensitive measurements of the generated two-photon field profile probed in an image plane of the two-photon source.