Violation of Bell's Inequality under Strict Einstein Locality Conditions

Abstract

We observe strong violation of Bell's inequality in an Einstein, Podolsky and Rosen type experiment with independent observers. Our experiment definitely implements the ideas behind the well known work by Aspect et al. We for the first time fully enforce the condition of locality, a central assumption in the derivation of Bell's theorem. The necessary space-like separation of the observations is achieved by sufficient physical distance between the measurement stations, by ultra-fast and random setting of the analyzers, and by completely independent data registration.The stronger-than-classical correlations between entangled quantum systems, as first discovered by Einstein, Podolsky and Rosen (EPR) in 1935 [1], have ever since occupied a central position in the discussions of the foundations of quantum mechanics. After Bell's discovery [2] that EPR's implication to explain the correlations using hidden parameters would contradict the predictions of quantum physics, a number of experimental tests have been performed [3][4][5]. All recent experiments confirm the predictions of quantum mechanics. Yet, from a strictly logical point of view, they don't succeed in ruling out a local realistic explanation completely, because of two essential loopholes. The first loophole builds on the fact that all experiments so far detect only a small subset of all pairs created [6]. It is therefore necessary to assume that the pairs registered are a fair sample of all pairs emitted. In principle this could be wrong and once the apparatus is sufficiently refined the experimental observations will contradict quantum mechanics. Yet we agree with John Bell that ". . . it is hard for me to believe that quantum mechanics works so nicely for inefficient practical set-ups and is yet going to fail badly when sufficient refinements are made. Of more importance, in my opinion, is the complete absence of the vital time factor in existing experiments. The analyzers are not rotated during the flight of the particles." [7] This is the second loophole which so far has only been encountered in an experiment by Aspect et al. [4] where the directions of polarization analysis were switched after the photons left the source. Aspect et al., however, used periodic sinusoidal switching, which is predictable into the future. Thus communication slower than the speed of light, or even at the speed of light [8] could in principle explain the results obtained. Therefore this second loophole is still open.The assumption of locality in the derivation of Bell's theorem requires that the measurement processes of the two observers are space-like separated (Fig. 1). This means that it is necessary to freely choose a direction for analysis, to set the analyzer and finally to register the particle such that it is impossible for any information about these processes to travel via any (possibly unknown) channel to the other observer before he, in turn, finishes his measurement [9]. Selection of an analyzer direction has to be completely unpredictable which necessitates a...

The ultimate physical limits of privacy

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Bell violation using entangled photons without the fair-sampling assumption

“…The two other main assumptions include "locality" (10,11) and "freedom of choice" (12). Invoking any of these renders an experiment vulnerable to explanation by a local realistic theory.…”

Quantum entanglement: facts and fiction – how wrong was Einstein after all?

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“…1 Bohm & Aharonov (1957) (Aspect et al 1982a, b;Clauser et al 1969;Clauser & Horne, 1974;Clauser & Shimony, 1978;Freedman & Clauser, 1972;Giustina et al 2015;Guerreiro et al 2012;Hensen et al 2015;Horne & Zeilinger, 1985;Kimble et al 1977;Weihs et al 1998;Zbinden et al 2001).…”