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arXiv:1608.02404

Anomalous Postselection in the Hensen et al. Bell Test

Donald A. Graft

Published Aug 8, 2016• 3 citations
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Abstract

It is shown that the data of the Hensen et al. Bell test experiment exhibits anomalous postselection that can fully account for the apparent violation of the CHSH inequality. A simulation of a local realist model implementing similar postselection is presented. The model produces an apparent violation of CHSH indistinguishable from that of the experiment. The experimental data also appears to violate no-signaling, and it is shown how postselection can produce an artifactual violation of no-signaling. The Hensen et al. experiment does not succeed in rejecting classical locality and therefore does not confirm quantum nonlocality.

DOI
10.48550/arxiv.1608.02404

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It is shown that the data of the Hensen et al. Bell test experiment exhibits anomalous postselection that can fully account for the apparent violation of the CHSH inequality. A simulation of a local realist model implementing similar postselection is presented. The model produces an apparent violation of CHSH indistinguishable from that of the experiment. The experimental data also appears to violate no-signaling, and it is shown how postselection can produce an artifactual violation of no-signaling. The Hensen et al. experiment does not succeed in rejecting classical locality and therefore does not confirm quantum nonlocality.
Recently Wang et al. have reported a violation of a Bell inequality without entanglement [arXiv:2507.07756]. We show that their result is an artifact of postselection. It is well known that postselection may yield Bell inequality violations, both in classical toy models and in real experiments with delayed-choice entanglement-swapping. Here we describe a classical analog of Wang et al.'s experiment, and show that it produces essentially the same results as their quantum version. We explain in detail why neither version is a challenge to Local Causality or local realism: the postselection entails a rejection of Bell's assumption of Statistical Independence.
The recent Bell test performed in Delft [B. Hensen et al. Nature 526, 682 (2015), arXiv:1508.05949], claimed as loophole-free, has shown violation of local realism with 96% confidence level. However, the raw data indicate violation of no-signaling principle (microcausality) around 99% confidence level. While violation of local realism is consistent with quantum mechanics, it is not the case of no-signaling. Violation of the latter would be a groundbreaking revolution in physics but also invalidate the conclusion of the Bell theorem, where it no-signaling assumed and must be verified or at least not falsified. If the signature of signaling is believed to be a statistical error, a fair calculation of the Bell parameter gives S = 1.86 < 2, in accordance with local realism. Therefore further experimental tests are urgent to clarify with better confidence level whether local realism or no-signaling is violated or none of them.
Violation of the CHSH inequality supposedly demonstrates an irreconcilable conflict between quantum mechanics and local, realistic hidden variable theories. We show that the mathematical assumptions underlying the proof of the CHSH inequality are, in fact, incompatible with the physics of the experiments testing such inequality. This implies that we cannot dismiss local realistic hidden variable theories on the basis of currently available experimental data yet. However, we also show that an experimental proof of CHSH inequality is, in principle, possible, but it is unclear how to implement, in practice, such an experiment.
The aim of this study is to produce a simulation of EPR experiments violating the CHSH-Bell inequalities using physically interpretable objects (properties defined before measurement) and interactions (no supraliminal communication), without influence from any theory. It turns out that the proposed model systematically violates the CHSH-Bell inequalities reaching all the values ( 2 ≤ S ≤ 4 ) . Our simulation reproduces experimental entanglements with greater efficiency. This approach has at least two consequences. First, it demonstrates that violations of the CHSH-Bell inequalities are possible while still verifying the principles of realism and locality, but in a different sense from that of Bell’s theorem. Therefore, Bell’s theorem itself is not called into question, nor are the results of the EPR experiments. However, it is the deduction that leads to the current interpretation (often described as strange because it does not follow one of the principles of realism and locality as defined by Bell’s theorem) that is challenged. Second, it challenges real-world EPR experiments to exceed the efficiency rates of our simulation. Our idealization demonstrates that, between the efficiency rates required to confirm the violation of Bell’s inequalities and the efficiency rates of our idealization, the interpretation of experiments remains possible within a framework of “classical” physical principles (properties defined before measurement and no supraliminal communication). Confirming the strangeness of quantum mechanics would therefore require obtaining efficiency rates higher than those of Bell’s theorem.