Quantum interference by a nonlocal double slit

We report an interference experiment in which photon pairs generated by spo ntaneous parametric down-conversion produce a Young-type fourth-order inter ference pattern after being scattered by two different and spatially separa ted apertures, whose superposition defines a double slit. The experiment is compared with previous ones based on parametric down-conversion, and its n onlocal nature is discussed. A theoretical explanation is also provided. [S 1050-2947(99)06507-5].