A method for demonstrating violation of local realism with a two-photon downconverter without use of Bell inequalities, J. Torgerson, D. Branning, L. Mandel, Applied Physics B 60 267-269 (1995)
Abstract. We show that the recent proposal by Hardy and Jordan for a test of local realism without the use of Bell inequalities can be implemented in two-photon coincident measurements with linear polarizes, when the photon pairs are produced by parametric downconversion. If the probabilities measured with real detectors are proportional to the corresponding probabilities determined with the idea detectors, this method does not depend on the use of detectors with high or even known quantum efficiencies.