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New Method to Reveal the Conflict Between Local Realism and Quantum Mechanics

Koji Nagata, Jaewook Ahn

Published Jan 1, 2007• 0 citations
OpenAlex

Abstract

We formulate the expectation value of the Bell-Żukowski operator acting on qubit states of a two-particle Bell experiment. By using the equivalence between a set of N copies of a two-qubit experiment and a standard two-setting Bell experiment in an entangled 2N-particle state, we obtain an inequality, which we may call the Bell-Żukowski inequality. It determines whether the measured correlation functions of two-particle states can be modeled locally and realistically. In this Bell experiment of two particles, the conflict between local realism and quantum mechanics is discussed in conjunction with the violation of the Bell-Żukowski inequality. The main point of the result is that the Bell-Żukowski operator can be represented by the Bell-Mermin operator. PACS numbers: 03.65.Ud, 03.67.Mn

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New Method to Reveal the Conflict Between Local Realism and Quantum Mechanics

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We formulate the expectation value of the Bell-Żukowski operator acting on qubit states of a two-particle Bell experiment. By using the equivalence between a set of N copies of a two-qubit experiment and a standard two-setting Bell experiment in an entangled 2N-particle state, we obtain an inequality, which we may call the Bell-Żukowski inequality. It determines whether the measured correlation functions of two-particle states can be modeled locally and realistically. In this Bell experiment of two particles, the conflict between local realism and quantum mechanics is discussed in conjunction with the violation of the Bell-Żukowski inequality. The main point of the result is that the Bell-Żukowski operator can be represented by the Bell-Mermin operator. PACS numbers: 03.65.Ud, 03.67.Mn
We formulate the expectation value of the Bell-Zukowski operator acting on qubit states of a two-particle Bell experiment. By using the equivalence between a set of N copies of a two-qubit experiment and a standard two-setting Bell experiment in an entangled 2N-particle state, we obtain an inequality, which we may call the Bell-Zukowski inequality. It determines whether the measured correlation functions of two-particle states can be modeled locally and realistically. In this Bell experiment of two particles, the conflict between local realism and quantum mechanics is discussed in conjunction with the violation of the Bell-Zukowski inequality. The main point of the result is that the Bell-Zukowski operator can be represented by the Bell-Mermin operator. The threshold visibility of two-particle interference analyzed in this scheme shows good agreement with the value to cause a violation of the Bell-Zukowski inequality.
We consider a two-particle/two-setting Bell experiment to visualize the conflict between Bell–Żukowski inequality and Bell–Mermin inequality. The experiment is reproducible by local realistic theories which are not rotationally invariant. We find that the average value of Bell–Żukowski operator is evaluated by the two-particle/two-setting Bell experiment in question. Bell–Żukowski inequality reveals that the constructed local realistic theories for the experiment are not rotationally invariant. The two-particle Bell experiment in question reveals the conflict between Bell–Żukowski inequality and Bell–Mermin inequality. Our analysis finds the threshold visibility for the two-particle interference to reveal the conflict noted above. The threshold visibility agrees with the value to obtain a violation of Bell–Żukowski inequality.
We investigate the violation factor of the original Bell-Mermin inequality. Until now, we have used an assumption that the results of measurement are . In this case, the maximum violation factor is as follows: and . The quantum predictions by n-partite Greenberger-Horne-Zeilinger state violate the Bell-Mermin inequality by an amount that grows exponentially with n. Recently, a new measurement theory is proposed [K. Nagata and T. Nakamura, International Journal of Theoretical Physics, 49, 162 (2010)]. The values of measurement outcome are . Here we use the new measurement theory. We consider a multipartite GHZ state. We use the original Bell-Mermin inequality. It turns out that the original Bell-Mermin inequality is satisfied irrespective of the number of particles. In this case, the maximum violation factor is as follows: and . Thus the original Bell-Mermin inequality is satisfied by the new measurement theory. We propose the following conjecture: All the two-orthogonal-settings experimental correlation functions admit local realistic theories irrespective of a state if we use the new measurement theory.
The Bell inequality constrains the outcomes of measurements on pairs of distant entangled particles. The Bell contradiction states that the Bell inequality is inconsistent with the calculated outcomes of these quantum experiments. This contradiction led many to question the underlying assumptions, viz. so-called realism and locality. The probability model underlying the Bell inequality is generally left implicit. We propose an explicit probability model for the CHSH version of the Bell experiment. This model has only two simultaneously observable detector settings per measurement, and therefore does not assume realism. The quantum expectation now becomes a conditional expectation, given the two detector settings. This probability model is in full agreement with both quantum mechanics and experiments. As a result, the model satisfies the Bell inequality; there are no so-called violations. We extend this model to include a hidden variable. This extended model is not Bell-separable. This non-separability implies that the model is non-deterministic or non-local (or both).
Bell's theorem, and inequalities that stem from it, address the conflict between the explanation of key experimental observations by quantum mechanics (QM) and by models expressing Locally Realistic (LR) properties, regardless of their inclusion or exclusion of hidden variables. To demonstrate the conflict between experimental results described by QM and LR models, a physical realization of the quantum state must be chosen. Entangled photons or electrons provide the most viable choices. In this work we consider a simplified version of a Bell inequality (BI) that focuses entirely on the physical state properties of photons in order to demonstrate the difference between QM and LR correlations. While the experiment we propose is in principle similar in intent to prior Bell inequality experiments, our version requires fewer measurements, and is more advantageous in its conceptual clarity.
Bell's inequality is established based on local realism. The violation of Bell's inequality by quantum mechanics implies either locality or realism or both are untenable. Leggett's inequality is derived based on nonlocal realism. The violation of Leggett's inequality implies that quantum mechanics is neither local realistic nor nonlocal realistic. The incompatibility of nonlocal realism and quantum mechanics has been currently confirmed by photon experiments. In our work, we propose to test Leggett's inequality using the Aharonov-Casher effect. In our scheme, four entangled particles emitted from two sources manifest a two-qubit-typed correlation that may result in the violation of the Leggett inequality, while satisfying the no-signaling condition for spacelike separation. Our scheme is tolerant to some local inaccuracies due to the topological nature of the Aharonov-Casher phase. The experimental implementation of our scheme can be possibly realized by a calcium atomic polarization interferometer experiment.