Experimental demonstration of the violation of local realism without Bell inequalities

We report on a two-photon coincidence experiment that demonstrates the violation of local realism, as defined by Einstein, Podolsky and Rosen, by about 45 standard deviations without explicit use of Bell inequalities. The experiment is an implementation of ideas put forward by Hardy and Jordan; it depends on showing that certain coincidence rates are zero while another rate is non-zero. (orig.)