Ladder Proof of Nonlocality for Two Spin-half Particles Revisited

In this paper we extend the ladder proof of nonlocality without inequalities for two spin-half particles given by Boschi et al (Boschi D et al 1997 Phys. Rev. Lett. 79 2755) to the case in which the measurement settings of the apparatus measuring one of the particles are different from the measurement settings of the apparatus measuring the other particle. It is shown that, in any case, the proportion of particle pairs for which the contradiction with local realism goes through is maximized when the measurement settings are the same for each apparatus. Also we write down a Bell inequality for the experiment in question which is violated by quantum mechanics by an amount which is twice as much as the amount by which quantum mechanics violates the Bell inequality considered in the above paper by Boschi et al . PACS numbers: 03.65.Ud, 03.65.Ta