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An experimental test of non-local realism

Nature volume 446, pages 871–875 (2007)Cite this article

A Corrigendum to this article was published on 13 September 2007

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Abstract

Most working scientists hold fast to the concept of ‘realism’—a viewpoint according to which an external reality exists independent of observation. But quantum physics has shattered some of our cornerstone beliefs. According to Bell’s theorem, any theory that is based on the joint assumption of realism and locality (meaning that local events cannot be affected by actions in space-like separated regions) is at variance with certain quantum predictions. Experiments with entangled pairs of particles have amply confirmed these quantum predictions, thus rendering local realistic theories untenable. Maintaining realism as a fundamental concept would therefore necessitate the introduction of ‘spooky’ actions that defy locality. Here we show by both theory and experiment that a broad and rather reasonable class of such non-local realistic theories is incompatible with experimentally observable quantum correlations. In the experiment, we measure previously untested correlations between two entangled photons, and show that these correlations violate an inequality proposed by Leggett for non-local realistic theories. Our result suggests that giving up the concept of locality is not sufficient to be consistent with quantum experiments, unless certain intuitive features of realism are abandoned.

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Figure 1: Testing non-local hidden-variable theories.
Figure 2: Experimental set-up.
Figure 3: Experimental violation of the inequalities for non-local hidden-variable theories (NLHV) and for local realistic theories (CHSH).

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Acknowledgements

We are grateful to A. J. Leggett for stimulating this work and for discussions. We also thank D. Greenberger, M. A. Horne, T. Jennewein, J. Kofler, S. Malin and A. Shimony for their comments. T.P. is grateful for the hospitality of the IQOQI, Vienna. M.A. thanks L. Gohlike for his hospitality at the Seven Pines VIII. We acknowledge support from the Austrian Science Fund (FWF), the European Commission, the Austrian Exchange Service (ÖAD), the Foundation for Polish Science (FNP), the Polish Ministry of Higher Education and Science, the City of Vienna and the Foundational Questions Institute (FQXi).

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Authors and Affiliations

  1. Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria,

    Simon Gröblacher, Rainer Kaltenbaek, Časlav Brukner, Marek Żukowski, Markus Aspelmeyer & Anton Zeilinger

  2. Institute for Quantum Optics and Quantum Information (IQOQI), Austrian Academy of Sciences, Boltzmanngasse 3, A-1090 Vienna, Austria,

    Simon Gröblacher, Časlav Brukner, Markus Aspelmeyer & Anton Zeilinger

  3. Institute of Theoretical Physics and Astrophysics, University of Gdansk, ul. Wita Stwosza 57, PL-08-952 Gdansk, Poland,

    Tomasz Paterek & Marek Żukowski

  4. The Erwin Schrödinger International Institute for Mathematical Physics (ESI), Boltzmanngasse 9, A-1090 Vienna, Austria,

    Tomasz Paterek

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Correspondence to Markus Aspelmeyer or Anton Zeilinger.

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Supplementary information

Supplementary Equations

This file contains Supplementary Equations. The authors give an explicit example of a nonlocal hidden-variable model that fulfils all assumptions of the considered class. It is shown that the model can explain existing Bell experiments. In the second part the authors provide a detailed derivation of the inequality for the class of theories. (PDF 193 kb)

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Gröblacher, S., Paterek, T., Kaltenbaek, R. et al. An experimental test of non-local realism. Nature 446, 871–875 (2007). https://doi.org/10.1038/nature05677

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