Violation of a Bell-type inequality in the homodyne measurement of light in an Einstein-Podolsky-Rosen state - art. no. 063804

An optical Einstein-Podolsky-Rosen (EPR) state is produced in the spontaneo us parametric down-conversion of an ultrashort classical pump pulse. It is shown both theoretically and experimentally that this results in the violat ion of a Bell-type inequality of the kind proposed by Grangier et al. The e xperiment is based on measuring interference between the light in the EPR s tate and weak light pulses in a coherent state. The maximum observed visibi lity of the interference pattern was (89+/-4)%. This interference can be re garded as a manifestation of nonlocality in the sense described by Banaszek and Wodkiewicz, even though the EPR state has a positive Wigner function. We develop the theory of two-channel homodyne detection with ultrafast puls es and then apply it to the EPR state generated in a type-II collinear geom etry. Particular attention is paid to the investigation of how dispersion a nd phase matching influence the violation of local realism.