2-PHOTON DOUBLE-SLIT INTERFERENCE EXPERIMENT

We report a two-photon double-slit interference experiment. Two correl ated photons, generated by spontaneous parametric downconversion and t raveling in different directions, are made to pass through a double sl it in such a way that the path of one photon can be identified with th at of the other photon. No single-photon interference pattern is obser ved even if the path is not actually identified, but a spatial interfe rence pattern appears in the joint detection counting rates of the pho ton pairs. It can easily be shown that these nonlocal phenomena cannot be exhibited by any kind of classical field. (C) 1998 Optical Society of America [S0740-3224(98)01003-0].