Critical analysis of the empirical tests of local hidden-variable theories

Santos, Emilio

doi:10.1103/physreva.46.3646

Cited by 136 publications

(85 citation statements)

References 31 publications

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“…It is possible to reproduce nonlocal correlations with a model that is Bell-local, but which violates the fair sampling assumption [17,18]. Denote the event that Alice's (Bob's) detector clicks by D A (D B ).…”

Section: Pacs Numbersmentioning

confidence: 99%

How Much Measurement Independence Is Needed to Demonstrate Nonlocality?

2011

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If nonlocality is to be inferred from a violation of Bell's inequality, an important assumption is that the measurement settings are freely chosen by the observers, or alternatively, that they are random and uncorrelated with the hypothetical local variables. We study the case where this assumption is weakened, so that measurement settings and local variables are at least partially correlated. As we show, there is a connection between this type of model and models which reproduce nonlocal correlations by allowing classical communication between the distant parties, and a connection with models that exploit the detection loophole. We show that even if Bob's choices are completely independent, all correlations obtained from projective measurements on a singlet can be reproduced, with the correlation (measured by mutual information) between Alice's choice and local variables less than or equal to a single bit. PACS numbers:Quantum nonlocality, whereby particles appear to influence one another instantaneously even though they are widely separated in space, is one of the most remarkable phenomena known to modern science [1][2][3][4]. Historically, this peculiar prediction of quantum theory triggered many debates and even doubts about its validity. Today, it is a well established experimental fact [5].The profound implications of quantum nonlocality for our world view remain controversial. But it is no longer considered as suspicious, or of marginal interest. It is central to our understanding of quantum physics, and in particular it is essential for the powerful applications of quantum information technologies. In 1991, A. Ekert showed how shared entanglement could enable distant partners to establish a shared cryptographic key [8]. Ekert's intuition is quite simple -if there are no local variables, then no adversary could possibly hold a copy of these variables -yet it came decades after the birth of quantum mechanics. In 2005, Barrett and co-workers used this intuition to show how, with no further assumptions about quantum theory, nonlocal correlations alone could ensure security of a secret key [9]. Acín and coworkers extended this result, showing how to generate secret keys using simple nonlocal correlations that violate the well-known CHSH inequality [10]. Simultaneously, it was realized that Bell inequalities are the only entanglement witnesses that can be trusted in cases where the dimensions of the relevant Hilbert spaces are unknown [10].In an experimental demonstration of quantum nonlocality, measurements are performed on separated quantum systems in an entangled state, and it is shown that the measurement outcomes are correlated in a manner that cannot be accounted for by local variables. In order to conclude that nonlocality is exhibited, it is crucial for the analysis that the choices of which measurement to perform are freely made by the experimenters. Alternatively, they must be random and uncorrelated with the hypothetical local variables. It is well known that if the measurement settings are not rand...

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Section: Pacs Numbersmentioning

confidence: 99%

How Much Measurement Independence Is Needed to Demonstrate Nonlocality?

2011

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“…Experimental violation [5][6][7][8][9][10][11][12][13][14][15] of Bell inequalities provides strong evidence against LHV theories, but almost all of these experiments (with the exceptions of those in Refs. [13,15]) have the loophole that the violation of the Bell inequality could, in principle, be caused by loss [16][17][18][19][20][21]. The interpretation of these experiments as ruling out LHV theories therefore relies on the assumption that the sampling is "fair" [3,22].…”

Section: Introductionmentioning

confidence: 99%

Fair-sampling assumption is not necessary for testing local realism

et al. 2010

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Almost all Bell inequality experiments to date have used postselection and therefore relied on the fair sampling assumption for their interpretation. The standard form of the fair sampling assumption is that the loss is independent of the measurement settings, so the ensemble of detected systems provides a fair statistical sample of the total ensemble. This is often assumed to be needed to interpret Bell inequality experiments as ruling out hidden-variable theories. Here we show that it is not necessary; the loss can depend on measurement settings, provided the detection efficiency factorizes as a function of the measurement settings and any hidden variable. This condition implies that Tsirelson's bound must be satisfied for entangled states. On the other hand, we show that it is possible for Tsirelson's bound to be violated while the Clauser-Horne-Shimony-Holt (CHSH)-Bell inequality still holds for unentangled states, and present an experimentally feasible example.

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“…This causes very low collection efficiency. Moreover, the entanglement is only perfect for photons that are emitted back to back, a loophole that could allow local hidden-variable model to explain the experimental data (Santos, 1991(Santos, , 1992. Meanwhile it was discovered that the process of spontaneous parametric down-conversion allows pairs of entangled photons to be collected in clearly specified directions, with reasonable intensity and with very high purity.…”

Section: Experimental Realizations Of Photonic Entanglementmentioning

confidence: 99%

Multiphoton entanglement and interferometry

Bourennane

Eibl

Gaertner

et al. 2003

Fortschritte der Physik

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Multi-photon interference reveals strictly non-classical phenomena. Its applications range from fundamental tests of quantum mechanics to photonic quantum information processing, where a significant fraction of key experiments achieved so far comes from multi-photon state manipulation. We review the progress, both theoretical and experimental, of this rapidly advancing research. The emphasis is given to the creation of photonic entanglement of various forms, tests of the completeness of quantum mechanics (in particular, violations of local realism), quantum information protocols for quantum communication (e.g., quantum teleportation, entanglement purification and quantum repeater), and quantum computation with linear optics. We shall limit the scope of our review to "few photon" phenomena involving measurements of discrete observables.

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Critical analysis of the empirical tests of local hidden-variable theories

Abstract: A local hidden-variable model is exhibited for the experiments by Aspect, Grangier, and Roger [Phys. Rev. Lett. 47, 460 (1981); 49, 91 (1982)

Cited by 136 publications

References 31 publications

How Much Measurement Independence Is Needed to Demonstrate Nonlocality?

How Much Measurement Independence Is Needed to Demonstrate Nonlocality?

Fair-sampling assumption is not necessary for testing local realism

Multiphoton entanglement and interferometry

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