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A local hidden variable model of quantum correlation exploiting the detection loophole

Gisin, Nicolas, Gisin, B V

Published Jan 1, 1999• 103 citations
OpenAlex

Abstract

A local hidden variable model exploiting the detection loophole to reproduce exactly the quantum correlation of the singlet state is presented. The model is shown to be compatible with both the CHSH and the CH Bell inequalities. Moreover, it bears the same rotational symmetry as spins. The reason why the model can reproduce the quantum correlation without violating the Bell theorem is that in the model the efficiency of the detectors depends on the local hidden variable. On average the detector efficiency is limited to 75%.

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A local hidden variable model exploiting the detection loophole to reproduce exactly the quantum correlation of the singlet state is presented. The model is shown to be compatible with both the CHSH and the CH Bell inequalities. Moreover, it bears the same rotational symmetry as spins. The reason why the model can reproduce the quantum correlation without violating the Bell theorem is that in the model the efficiency of the detectors depends on the local hidden variable. On average the detector efficiency is limited to 75%.
A local hidden-variable model is constructed for the postselected correlations of nonmaximally entangled photon pairs in the states |Phi_r> and |Psi_r>, continuous in r over [-1,1] from the product state to the maximally entangled state. Its root-mean-square deviations from the quantum correlations and from the coincidence probabilities, averaged over a uniform grid of polarizer angles, are 0.0322 and 0.0233, smaller than those of the sigmoid-threshold model of Ref. [14] by factors of 2.7 to 3.5. The source emits a photon pair with a probability that depends on the hidden variable and on r; each station detects with a probability that depends on the local hidden variable and on the local polarizer angle. This dependence violates the fair-sampling assumption and exploits the detection loophole. On the postselected sample the model violates the CHSH inequality for |Phi_r>, reaching 2*sqrt(2) at |r|=1, with single-detector efficiency ≈ 85%, outside the assumptions of both the CHSH inequality and Mermin's 82.8% efficiency bound. The CH--Eberhard parameter, which does not assume fair sampling, satisfies J<0 over the full entanglement range.
An alternative method of detection-loophole-free Bell test is proposed using local hidden variable (LHV) models with optimal detection efficiencies. A framework for constructing such optimal LHV models is presented. Optimal LHV models for maximally and non-maximally entangled twopartite states are constructed to reproduce the quantum correlations within the critical detection efficiencies. The LHV models are shown to be completely equivalent with the existing twopartite Bell inequalities in their optimized setups, and to have even lower critical efficiencies in the LHV modes' own optimized setups. Applications in Bell tests and in device-independent quantum information processing are discussed.
Bell’s theorem presents a fundamental limit on the correlations achievable by any local hidden variable theory, seemingly precluding such models from reproducing quantum mechanical predictions. In this paper, we introduce a local hidden variable model based on phenomenological velocity and curvature operator techniques. By constructing a mathematical framework that maintains locality and realism, we demonstrate that it is possible to reproduce the quantum mechanical correlation functions that violate Bell’s inequalities. This challenges the conventional understanding imposed by Bell’s theorem and suggests the need for a re-examination of the foundational assumptions in quantum mechanics.
Bell's theorem is supposed to exclude all local hidden-variable models of quantum correlations.However, an explicit counterexample shows that a new class of local realistic models, based on generalized arithmetic and calculus, can exactly reconstruct rotationally symmetric quantum probabilities typical of two-electron singlet states.Observable probabilities are consistent with the usual arithmetic employed by macroscopic observers but counterfactual aspects of Bell's theorem are sensitive to the choice of hidden-variable arithmetic and calculus.The model is classical in the sense of Einstein, Podolsky, Rosen and Bell: elements of reality exist and probabilities are modeled by integrals of hidden-variable probability densities.Probability densities have a Clauser-Horne product form typical of local realistic theories.However, neither the product nor the integral nor the representation of rotations are the usual ones.The integral has all the standard properties but only with respect to the arithmetic that defines the product.Certain formal transformations of integral expressions found in the usual proofs à la Bell do not work, so standard Bell-type inequalities cannot be proved.The system we deal with is deterministic, local-realistic, rotationally invariant, observers have free will, detectors are perfect, hence the system is free of all the canonical loopholes discussed in the literature.