On EPR paradox, and violation of the Bell inequality in local quantum mechanics

Apoorva Patel

Sergio Doplicher

David K. Ferry

From the early days of quantum mechanics, there has been a discussion on the concept of reality, exemplified by the EPR paradox. To many, the idea of the paradox and the possibility of local hidden variables was dismissed by the Bell inequality. Yet, there remains considerable evidence that this inequality can be violated even by classical systems, so that experiments showing quantum behavior and the violation of the inequality must be questioned. Here, we demonstrate that classical optical polarization experiments can be shown to violate the Bell inequality. Hence, such experiments cannot be used to distinguish between classical and quantum theories.

Pankaj Sharan

S. Rajasekar, R. Velusamy

Quantum theory is considered as the most successful scientific theory of all time. The realization of a controversy between quantum mechanics and reasonable assumptions was pointed out by Einstein, Boris Podolsky and Nathan Rosen (EPR) in 1935. It was John Stewart Bell, an Irish physicist, established what the quantum theory can tell us about the nature of the world. Bell formulated certain inequalities based on the arguments of EPR. They should be valid for any theory satisfying the notions of reality and locality. The striking news is that the Bell's inequality is violated by quantum mechanics but the experimental results agree with the predictions of quantum theory. This chapter presents the Schrodinger cat paradox and Bohm's version of EPR paradox. It gives a brief sketch of Bell's inequality and the quantum mechanical examples violating it. Most of the experiments were based on correlations between the polarizations of pairs of photons. Correlated photons can be produced in many ways.

Philippe Grangier