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Are quantum correlations local elements of reality? A Bell inequality to test this

Michael Seevinck

Published Aug 23, 2005• 0 citations
OpenAlex

Abstract

We show, using a Bell inequality argument, that quantum correlations cannot be regarded as local elements of reality. It is well known since the work of J.S. Bell, that one cannot have locally preexistent values for all physical quantities, whether they are deterministic or stochastic. The Bell inequality argument we present here shows this is also impossible for correlations among subsystems of an individual isolated composite system. Thus there is no philosophical difference with respect to questions of locality and realism between correlations on the one hand and values of quantities on the other hand that could allow one to have a different view about their ontological status. Neither of them can be used to build up a world consisting of some local realistic structure. This argument has an important advantage over others who use so-called Greenberger-Horne-Zeilinger and Hardy type arguments because it does not need perfect correlations but only statistical correlations. It can therefore easily be tested in currently feasible experiments using four particle entanglement.

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We show, using a Bell inequality argument, that quantum correlations cannot be regarded as local elements of reality. It is well known since the work of J.S. Bell, that one cannot have locally preexistent values for all physical quantities, whether they are deterministic or stochastic. The Bell inequality argument we present here shows this is also impossible for correlations among subsystems of an individual isolated composite system. Thus there is no philosophical difference with respect to questions of locality and realism between correlations on the one hand and values of quantities on the other hand that could allow one to have a different view about their ontological status. Neither of them can be used to build up a world consisting of some local realistic structure. This argument has an important advantage over others who use so-called Greenberger-Horne-Zeilinger and Hardy type arguments because it does not need perfect correlations but only statistical correlations. It can therefore easily be tested in currently feasible experiments using four particle entanglement.
The authors survey what is known about correlations in physical systems. Bell (1964-6) found that locally realistic theories are limited in the types of correlations which they allow. The more recent results of Greenberger, Horne and Zeilinger (1992) and of Hardy (1989) have shown that local realism imposes even stronger restrictions than those found by Bell. It is less well known that quantum mechanics is also limited in the kinds of correlations it can produce. This was first discovered by Tsirelson (1980). The authors discuss Tsirelson's results and related work by Landau (1987). They conclude by presenting further conditions which quantum mechanical correlations must satisfy.
Most physicists agree that the Einstein–Podolsky–Rosen–Bell paradox exemplifies much of the strange behavior of quantum mechanics, but argument persists about what assumptions underlie the paradox. To clarify what the debate is about, we employ a simple and well-known thought experiment involving two correlated photons to help us focus on the logical assumptions needed to construct the EPR and Bell arguments. The view presented in this paper is that the minimal assumptions behind Bell’s inequality are locality and counterfactual definiteness but not scientific realism, determinism, or hidden variables as are often suggested. We further examine the resulting constraints on physical theory with an illustration from the many-worlds interpretation of quantum mechanics—an interpretation that we argue is deterministic, local, and realist but that nonetheless violates the Bell inequality.
The experimental test of the CHSH inequality confirms the quantum-mechanically predicted perfect correlations between two spatially separated photons. By interpreting the correlations non-locally as the so-called entanglement, Bell's theorem denies the existence of definite polarizations possessed by photons in the absence of measurement. The denial amounts to refuting Einstein's argument for defending his local-realist world view in the Einstein-Bohr debate on the conceptual foundations of quantum mechanics. Einstein's argument is based on his separability principle and his ensemble interpretation of ψ-functions. This paper shows that Bell's theorem is incorrect, and an explanation of the correlations based on Einstein's argument is given. As shown by the explanation based on Einstein's argument, the correlations are deterministic. A formal analysis supporting Einstein's explanation is also presented.
Starting from the late 60’s many experiments have been performed to verify the violation Bell’s inequality by Einstein-Podolsky-Rosen (EPR) type correlations. The idea of these experiments being that: (i) Bell’s inequality is a consequence of locality, hence its experimental violation is an indication of non locality; (ii) this violation is a typical quantum phenomenon because any classical system making local choices (either deterministic or random) will produce correlations satisfying this inequality. Both statements (i) and (ii) have been criticized by quantum probability on theoretical grounds (not discussed in the present paper) and the experiment discussed below has been devised to support these theoretical arguments. We emphasize that the goal of our experiment is not to reproduce classically the EPR correlations but to prove that there exist perfectly local classical dynamical systems violating Bell’s inequality. The conclusions of the present experiment are: no contradiction between quantum theory and locality can be deduced from the violation of Bell’s inequality. The Copenhagen interpretation of quantum theory becomes quite reasonable and not metaphyisic if interpreted at the light of the chameleon effect. One can realize quantum entanglement by classical computers. In section (7) we prove that our experiment also provides a classical analogue of the type of logical (i.e. independent of statistics) incompatibilities pointed out by Greenberger, Home and Zeilinger. These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
The experimental test of the CHSH inequality confirms the quantum-mechanically predicted perfect correlation between two spatially separated photons. By interpreting the correlation non-locally as the so-called entanglement, Bell's theorem denies the existence of definite polarizations possessed by photons in the absence of measurement. The denial amounts to refuting Einstein's argument for defending his local-realist world view based on his separability principle and his ensemble interpretation of ψ-functions in the Einstein-Bohr debate on the conceptual foundations of quantum mechanics. This paper shows that Bell's theorem is incorrect and presents an explanation of the correlation based on Einstein's argument. The correlation is deterministic. A formal analysis supporting Einstein's explanation is also presented.
The experimental test of the CHSH inequality confirms the quantum-mechanically predicted perfect correlation between two spatially separated photons. By interpreting the correlation non-locally as the so-called entanglement, Bell's theorem denies the existence of definite polarizations possessed by photons in the absence of measurement. The denial amounts to refuting Einstein's argument for defending his local-realist world view based on his separability principle and his ensemble interpretation of ψ-functions in the Einstein-Bohr debate on the conceptual foundations of quantum mechanics. This paper shows that Bell's theorem is incorrect and presents an explanation of the correlation based on Einstein's argument. The correlation is deterministic. A formal analysis supporting Einstein's explanation is also presented.