Experimental test of the violation of local realism in quantum mechanics without Bell inequalities

We report the results of an experiment in which postselected polarization-entangled photons were used to test the recent nonlocality proof by L. Hardy [Phys. Rev. Lett. 71, 1665 (1993)]. The particular source of entangled photons used in the experiment has the advantage that it is very easy to prepare a pair of photons in a state with any degree of entanglement. Hardy’s theorem, which only works for nonmaximally entangled states, was tested for a range of states.