Bell's theorem and the nature of reality

We rediscuss the Einstein-Podolsky-Rosen paradox in Bohm's spin version and oppose to it Bohr's controversial point of view. Then we explain Bell's theorem, Bell inequalities, and its consequences. We describe the experiment of Aspect, Dalibard, and Roger in detail. Finally we draw attention to the nonlocal structure of the underlying theory.Dedicated to J. S. Bell on his 60th birthday.     

EPR and Bell's theorem: A critical review

The argument of Einstein, Podolsky, and Rosen is reviewed with attention to logical structure and character of assumptions. Bohr's reply is discussed. Bell's contribution is formulated without use of hidden variables, and efforts to equate hidden variables to realism are critically examined. An alternative derivation of nonlocality that makes no use of hidden variables, microrealism, counterfactual definiteness, or any other assumption alien to orthodox quantum thinking is described in detail, with particular attention to the quartet or broken-square question.     

Whiteheadian approach to quantum theory and the generalized Bell's theorem

The model of the world proposed by Whitehead provides a natural theoretical framework in which to imbed quantum theory. This model accords with the ontological ideas of Heisenberg, and also with Einstein's view that physical theories should refer nominally to the objective physical situation, rather than our knowledge of that system. Whitehead imposed on his model the relativistic requirement that what happens in any given spacetime region be determined only by what has happened in its absolute past, i.e., in the backward light-cone drawn from that region. This requirement must be modified, for it is inconsistent with the implications of quantum theory expressed by a generalized version of Bell's theorem. Revamping the causal spacetime structure of the Whitehead-Heisenberg ontology to bring it into accord with the generalized Bell's theorem creates the possibility of a nonlocal causal covariant theory that accords with the statistical prediction of quantum theory.Based on lectures given at the University of Texas, March–May 1977. This work was supported in part by the United States Energy Research and Development Agency, in part by the University of Texas, and in part by CERN.     

Experimentally testing Bell’s theorem based on Hardy’s nonlocal ladder proofs

Bell's theorem argues the existence of quantum nonlocality which goes basically against the hidden variable theory(HVT). Many experiments have been done via testing the violations of Bell's inequalities to statistically verify the Bell's theorem. Alternatively,by testing the Hardy's ladder proofs we experimentally demonstrate the deterministic violation of HVT and thus confirm the quantum nonlocality. Our tests are implemented with non-maximal entangled photon pairs generated by spontaneous parametric down conversions(SPDCs). We show that the degree freedom of photon entanglement could be significantly enhanced by using interference filters. As a consequence, the Hardy's ladder proofs could be tested and Bell's theorem is verified robustly. The probability of violating the locality reach to 41.9%, which is close to the expectably ideal value 46.4% for the photon pairs with degree of entanglement ε = 0.93. The higher violating probability is possible by further optimizing the experimental parameters.     

Generalization of Bell's theorem

A concise proof of Bell's theorem on the necessary nonlocality of any theory which models individual measurements in correlated quantum mechanical systems is presented. A family of inequalities is derived which may be applied to a broad class of correlated systems to test the assumption of locality.     

On the real meaning of Bell's theorem

In the last couple of years many important results have been derived showing that Bell's inequalities are nothing else but the indicator whether certain events and their probabilities can be represented or not within a Kolmogorovian probabilistic model. It has become evident that one can derive the Bell's inequalities without mentioning locality, causality hidden variable, etc. Many authors jumped to conclusion that the original content of the Bell's theorem had lost its meaning. I reconsider original problem posed by Bell and I show that the Bell's theorem is still valid.1. On leave from the Institute for Theoretical Physics, Eötvös University, Budapest.     

On the real meaning of Bell's theorem

In the last couple of years many important results have been derived showing that Bell's inequalities are nothing else but the indicator of whether certain events and their probabilities can be represented within a Kolmogorovian probabilistic model. It has become evident that one can derive Bell's inequalities without mentioning locality, causality, hidden variables, etc. Many authors jumped to the conclusion that the original content of Bell's theorem had lost its meaning. I reconsider the original problem posed by Bell and I show that Bell's theorem is still valid.On leave from the Institute for Theoretical Physics, Eötvös University, Budapest, Hungary.     

Interpretation of the quantum formalism and Bell's theorem

It is argued that quantum mechanics must be interpreted according to the Copenhagen interpretation. Consequently the formalism must be used in a purely operational way. The relation between realism, hidden variables, and the Bell inequalities is discussed. The proof of impossibility of local hidden-variables theories (Bell's theorem) is criticized on the basis that the quantum mechanical states violating local realism are not physically realizable states.Einstein had great difficulty in reaching a sharp formulation of Bohr's meaning. What hope then for the rest of us.—John S. Bell (Ref. 1, p. 189).     

International Conference on Bell's theorem and the foundations of modern physics

First Announcement

International Conference on Bell's theorem and the foundations of modern physics     

Bipartite all-versus-nothing proofs of Bell's theorem with single-qubit measurements

If n qubits were distributed between 2 parties, which quantum pure states and distributions of qubits would allow all-versus-nothing (or Greenberger-Horne-Zeilinger-like) proofs of Bell's theorem using only single-qubit measurements? We show a necessary and sufficient condition for the existence of these proofs for any number of qubits, and provide all distinct proofs up to n=7 qubits. Remarkably, there is only one distribution of a state of n=4 qubits, and six distributions, each for a different state of n=6 qubits, which allow these proofs.     

Violation of Bell's inequality by a generalized einstein-podolsky-rosen state using homodyne detection

Using homodyning with weak coherent fields and photon counting, we have observed violations of Bell-type inequalities by the generalized Einstein-Podolsky-Rosen state produced in a pulsed nondegenerate optical parametric amplifier, as predicted by Grangier et al. [Phys. Rev. A 38, 3132 (1988)]. The maximum observed visibility of the interference pattern was (89+/-4)%. This interference can be regarded as a manifestation of nonlocality in the sense described by Banaszek and Wodkiewicz [Phys. Rev. A 58, 4345 (1998)]. We have investigated the interference both theoretically and experimentally and have measured the influence of dispersion and phase matching.     

一种基于特征值修正的盖尔圆变换信息论判源方法

本文在盖尔圆-信息论(GAIC)方法的基础上,提出了一种基于盖尔圆半径修正的目标数目判断方法。将特征值和盖尔圆半径结合作为修正的特征值,并将修正后的特征值应用于GAIC方法。这种盖尔圆半径修正的GAIC(MGAIC)方法检测性能稳定,克服了AIC在高信噪比下不是目标数目的一致估计的缺点且在低信噪比时检测性能优于GAIC,尤其在目标角度间隔较小或多目标强度不等时MGAIC表现出明显的优势,适合于多目标对抗的复杂环境。仿真实验和实际数据处理结果验证了所提算法的有效性。     

Bell's theorem: Proposition of realizable experiment using linear momenta

A proposition of a realizable experiment using linear momenta for testing the Bell inequalities is presented. The proposed experimental setup employs only standard modern optical devices.     

Comments on “locality,Bell's theorem,and quantum mechanics”

Two different ideas of locality are described. Both are due essentially to einstein. Quantum theory is compatible with the first but not the second. The problems encountered in the article cited in the title arise from trying to use only the first idea of locality, whereas Bell's-theorem considerations pertain to the second.     

A remark on the generalized Goldberg-Sachs theorem

Despite the elegant formulations of Kundt and Thompson[1], and Robinson and Schild[2], it is not obvious how general the generalized GoldbergSachs theorem[3] really is. A spacetime satisfying Einstein's equations with a null fluid source, for example, can elude the generalized theorem if, and only if, the null direction of the fluid is a fourfold repeated principal null direction of the Weyl tensor. An example of such a spacetime is presented.     

Bell's expression and the generalized Garg form for forced dissociation of a biomolecular complex

The dissociation of a biomolecular complex under the action of constant force, constant loading rate, and periodic force is studied theoretically. We show that the celebrated Bell expression provides a good approximation for the bond dissociation rate when F/F(c)<1, where F(c) is the maxima slope of the binding potential along the reaction coordinate. When 1-F/F(c) <1 the dissociation rate is better described by a generalized Garg form in which the potential derivative is expanded near F(c). We also show that a constant-force experiment is suitable for extracting the activation energy of the bond, a constant loading experiment is suitable to extract F(c), while time-periodic force can be applied to extract both bond dissociation rates at zero force and F(c).