Optical tests of Bell’s inequalities not resting upon the absurd fair sampling assumption,(2004) (original) (raw)

Challenging preconceptions about Bell tests with photon pairs

Physical Review A, 2015

Motivated by very recent experiments, we consider a scenario "à la Bell" in which two protagonists test the Clauser-Horne-Shimony-Holt (CHSH) inequality using a photon-pair source based on spontaneous parametric down conversion and imperfect photon detectors. The conventional wisdom says that (i) if the detectors have unit efficiency, the CHSH violation can reach its maximum quantum value 2 √ 2. To obtain the maximal possible violation, it suffices that the source emits (ii) maximally entangled photon pairs (iii) in two well defined single modes. Through a non-perturabive calculation of non-local correlations, we show that none of these statements are true. By providing the optimal pump parameters, measurement settings and state structure for any detection efficiency and dark count probability, our results give the recipe to close all the loopholes in a Bell test using photon pairs.

Experimental confirmation of Bell inequality violations between entangled photon pairs

In order to confirm the validity of the entanglement hypothesis as predicted by quantum theory, counter to Einstein, Podolsky and Rosen’s objections as outlined in, we conducted detailed laboratory experiments to measure correlations between pairs of photons generated through parametric down conversion. Bell’s theorem, which states that no physical theory of local hidden variables can reproduce all of the predictions of quantum mechanics, was tested, and confirmed, by our experimental results.

Significant-Loophole-Free Test of Bell's Theorem with Entangled Photons

Physical review letters, 2015

Local realism is the worldview in which physical properties of objects exist independently of measurement and where physical influences cannot travel faster than the speed of light. Bell's theorem states that this worldview is incompatible with the predictions of quantum mechanics, as is expressed in Bell's inequalities. Previous experiments convincingly supported the quantum predictions. Yet, every experiment requires assumptions that provide loopholes for a local realist explanation. Here, we report a Bell test that closes the most significant of these loopholes simultaneously. Using a well-optimized source of entangled photons, rapid setting generation, and highly efficient superconducting detectors, we observe a violation of a Bell inequality with high statistical significance. The purely statistical probability of our results to occur under local realism does not exceed 3.74×10^{-31}, corresponding to an 11.5 standard deviation effect.

Violation of bell's inequalities with a local theory of photons

Foundations of Physics …, 1996

We use a local theory of photons purely as particles to model the single-photon experiment proposed by Tan, Walls, and Collett. Like Tan et al. we are able to derive a violation of Bell's inequalities for photon counts coincidence measurements. Our local probabilistic theory does not use any specific quantum mechanical calculations.

Tests of Bell inequality with arbitrarily low photodetection efficiency and homodyne measurements

Physical Review A, 2012

We show that hybrid local measurements combining homodyne measurements and photodetection provide violations of a Bell inequality with arbitrarily low photodetection efficiency. This is shown in two different scenarios: when one part receives an atom entangled to the field mode to be measured by the other part and when both parts make similar photonic measurements. Our findings definitely put the hybrid measurement scenario as a strong candidate for the implementation of a loophole-free Bell test. PACS numbers: 03.65.Ud,03.67.Mn

On Epr Paradox, Bell's Inequalities and Experiments that Prove Nothing

Old and New Concepts of Physics, 2008

This article shows that the there is no paradox. Violation of Bell's inequalities should not be identified with a proof of non locality in quantum mechanics. A number of past experiments is reviewed, and it is concluded that the experimental results should be re-evaluated. The results of the experiments with atomic cascade are shown not to contradict the local realism. The article points out flaws in the experiments with down-converted photons. The experiments with neutron interferometer on measuring the "contextuality" and Bell-like inequalities are analyzed, and it is shown that the experimental results can be explained without such notions. Alternative experiment is proposed to prove the validity of local realism.

Bell theorem without inequalities for two particles. I. Efficient detectors

Physical Review A, 2008

We again consider (as in a companion paper) an entangled two-particle state that is produced from two independent down-conversion sources by the process of "entanglement-swapping", so that the particles have never met. We show that there is a natural extension of the Einstein-Pololsky-Rosen discussion of "elements of reality" to include inefficient detectors. We consider inefficient deterministic, local, realistic models of quantum theory that are "robust", which we consider to be the minimum requirement for them to be taken seriously. By robust, we mean they satisfy the following three criteria: (a) they reproduce the quantum results for perfect correlations, if all particles are detected; (b) they produce some counts for every setting of the angles (so they don't describe some experiments that can easily be performed as "impossible"); (c) all their hidden variables are relevant (they must each produce a detectable result in some experiment). For such models we prove a Greenberger-Horne-Zeilinger (GHZ) type theorem for arbitrary detection efficiencies, showing that any such theory is inconsistent with the quantum mechanical perfect correlations. This theorem holds for individual events with no inequalities. As a result, the theorem is also independent of any random sampling hypothesis, and we take it as a refutation of such realistic theories, free of the detection efficiency and random sampling "loopholes". The hidden variable analysis depends crucially on the use of two independent laser sources for the down-conversions. We also investigate the necessity of using two independent sources vs a single source for all particles. Finally, we argue that the state we use can legitimately be considered as a two-particle state, and used as such in experiments.