BibTeX Source

@Article{Salart2008,
  author =       "D. Salart and A. Baas and C. Branciard and N. Gisin and H. Zbinden",
  title =        "Testing the speed of 'spooky action at a distance'",
  journal =      "Nature",
  year =         "2008",
  volume =       "454",
  pages =        "861--864",
  number =       "7206",
  abstract =     "Correlations are generally described by one of two mechanisms: either a first
                 event influences a second one by sending information encoded in bosons or other
                 physical carriers, or the correlated events have some common causes in their shared
                 history. Quantum physics predicts an entirely different kind of cause for some
                 correlations, named entanglement. This reveals itself in correlations that violate
                 Bell inequalities (implying that they cannot be described by common causes) between
                 space-like separated events (implying that they cannot be described by classical
                 communication). Many Bell tests have been performed(1), and loopholes related to
                 locality(2-4) and detection(5,6) have been closed in several independent
                 experiments. It is still possible that a first event could influence a second, but
                 the speed of this hypothetical influence (Einstein's 'spooky action at a distance')
                 would need to be defined in some universal privileged reference frame and be
                 greater than the speed of light. Here we put stringent experimental bounds on the
                 speed of all such hypothetical influences. We performed a Bell test over more than
                 24 hours between two villages separated by 18 km and approximately east-west
                 oriented, with the source located precisely in the middle. We continuously observed
                 two-photon interferences well above the Bell inequality threshold. Taking advantage
                 of the Earth's rotation, the configuration of our experiment allowed us to
                 determine, for any hypothetically privileged frame, a lower bound for the speed of
                 the influence. For example, if such a privileged reference frame exists and is such
                 that the Earth's speed in this frame is less than 10(-3) times that of the speed of
                 light, then the speed of the influence would have to exceed that of light by at
                 least four orders of magnitude.",
  doi =          "10.1038/nature07121",
  owner =        "cc",
  sn =           "0028-0836",
  timestamp =    "2010.08.20",
  ut =           "WOS:000258398600030",
}