We have a new paper out (online) in Nature Photonics today entitled, Experimental three-photon quantum nonlocality under strict locality conditions, by Chris Erven, Evan Mayer-Scott, Kent Fisher, Jonathan Lavoie, Brendon Higgins, Zhizhong Yan, Chris Pugh, Jean-Phillipe Bourgoin, Robert Prevedel, Krister Shalm, Laura Richards, Nick Gigov, Raymond Laflamme, Gregor Weihs, Thomas Jennewein, and Kevin Resch. This paper is the result of a great collaboration between three IQC groups and a former IQC faculty member, now at University of Innsbruck.
Abstract: Quantum correlations, often observed as violations of Bell inequalities, are critical to our understanding of the quantum world, with far-reaching technologicaland fundamental impact. Many tests of Bell inequalities have studied pairs of correlated particles. However, interest in multi-particle quantum correlations is driving the experimental frontier to test larger systems. All violations to date require supplementary assumptions that open results to loopholes, the closing of which is one of the most important challenges in quantum science. Seminal experiments have closed some loopholes, but no experiment has closed locality loopholes with three or more particles. Here, we close both the locality and freedom-of-choice loopholes by distributing three-photon Greenberger–Horne–Zeilinger entangled statesto independent observers. We measured a violation of Mermin’s inequalitywith parameter 2.77 ± 0.08, violating its classical bound by nine standard deviations. These results are a milestone in multi-party quantum communication and a significant advancement of the foundations of quantum mechanics.
Update April 16, 2014: Geoff Pryde discussed our work in a Nature Photonics News and Views article Entanglement à trois