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Violation of local realism with freedom of choice

  1. Anton Zeilingera,b,1
  1. aInstitute for Quantum Optics and Quantum Information, Austrian Academy of Sciences, Boltzmanngasse 3, 1090 Vienna, Austria; and
  2. bFaculty of Physics, University of Vienna, Boltzmanngasse 5, 1090 Vienna, Austria

  • ↵2Present address: Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom.

  • ↵3Present address: Department of Physics and Centre for Quantum Computer Technologies, University of Queensland, Brisbane QLD 4072, Australia.

  • ↵4Present address: Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom.

  • ↵5Present address: Institute of Quantum Computing, University of Waterloo, 200 University Avenue West, Waterloo, ON, Canada N2L 3G1.

  1. Edited by William D. Phillips, National Institute of Standards and Technology, Gaithersburg, MD, and approved September 15, 2010 (received for review March 4, 2010)

Abstract

Bell’s theorem shows that local realistic theories place strong restrictions on observable correlations between different systems, giving rise to Bell’s inequality which can be violated in experiments using entangled quantum states. Bell’s theorem is based on the assumptions of realism, locality, and the freedom to choose between measurement settings. In experimental tests, “loopholes” arise which allow observed violations to still be explained by local realistic theories. Violating Bell’s inequality while simultaneously closing all such loopholes is one of the most significant still open challenges in fundamental physics today. In this paper, we present an experiment that violates Bell’s inequality while simultaneously closing the locality loophole and addressing the freedom-of-choice loophole, also closing the latter within a reasonable set of assumptions. We also explain that the locality and freedom-of-choice loopholes can be closed only within nondeterminism, i.e., in the context of stochastic local realism.

Footnotes

  • 1To whom correspondence may be addressed. E-mail: johannes.kofler{at}univie.ac.at and anton.zeilinger{at}univie.ac.at.

  • Author contributions: T.S., R.U., J.K., S.R., X.-S.M., T.H., L.R., A.F., N.K.L., T.J., and A.Z. designed and performed research, analyzed data, and contributed to writing the paper.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission.

Freely available online through the PNAS open access option.

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