Demonstration of the complementarity of one- and two-photon interference -art. no. 063803

The visibilities of second-order (one-photon) and fourth-order (two-photon) interference have been observed in a Young's double-slit experiment using light generated by spontaneous parametric down-conversion and a photon-coun ting intensified charge-coupled device camera. Coherence and entanglement u nderlie one- and two-photon interference, respectively. As the effective so urce size is increased, coherence is diminished while entanglement is enhan ced, so that the visibility of one-photon interference decreases while that of two-photon interference increases. This experiment demonstrates the com plementarity between one- and two-photon interference (coherence and entang lement) in the spatial domain.