BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:Quantum correlations in Newtonian space and time: faster than ligh
 t communication or nonlocality - Gisin\, N (Universit de Genve)
DTSTART:20131016T080000Z
DTEND:20131016T090000Z
UID:TALK48190@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:Using a theorem that allows one to assert the presence of nonl
 ocal correlations between parties that are never measured in the same run 
 of an experiment (using marginal)\, we study the following question: Exper
 imental violations of Bell inequalities using space-like separated measure
 ments precludes the explanation of quantum correlations through causal inf
 luences propagating at subluminal speed. Yet\, everything looks as if the 
 two parties somehow communicate behind the scene. We investigate the assum
 ption that they do so at a speed faster than light\, though finite. Such a
 n assumption doesnt respect the spirit of Einstein relativity. However\, i
 t is not crystal clear that such communication behind the scene would cont
 radict relativity. Indeed\, one could imagine that this communication rema
 ins for ever hidden to humans\, i.e. that it could not be controlled by hu
 mans\, only Nature exploits it to produce correlations that cant be explai
 ned by usual common causes. To define faster than light hidden communicati
 on requires a universal privileged reference frame in which this faster th
 an light speed is defined. Again\, such a universal privilege d frame is n
 ot in the spirit of relativity\, but it is also clearly not in contradicti
 on: for example the reference frame in which the cosmic microwave backgrou
 nd radiation is isotropic defines such a privileged frame. Hence\, a prior
 i\, a hidden communication explanation is not more surprising than nonloca
 lity. We prove that for any finite speed\, such models predict correlation
 s that can be exploited for faster-than-light communication. This superlum
 inal communication doesnt require access to any hidden physical quantities
 \, but only the manipulation of measurement devices at the level of our pr
 esent-day description of quantum experiments. Consequently\, all possible 
 explanations of quantum correlations that satisfy the principle of continu
 ity\, which states that everything propagates gradually and continuously t
 hrough space and time\, or in other words\, all combination of local commo
 n causes and direct causes that reproduce quantum correlations\, lead to f
 aster than light communication\, which can be exploited by humans\, at lea
 st in principle. Accordingly\, either there is superluminal communication 
 or the conclusion that Nature is nonlocal (i.e. discontinuous) is unavoida
 ble.\n\n1. Jean-Daniel Bancal\, Stefano Pironio\, Antonio Acin\, Yeong-Che
 rng Liang\, Valerio Scarani and Nicolas Gisin\, Quantum non-locality based
  on finite-speed causal influences leads to superluminal signalling\, Natu
 re Physics\, 8\, 867-70\, 2012. 2. N. Gisin\, arXiv:1210.7308 3. Tomer Jac
 k Barnea\, Jean-Daniel Bancal\, Yeong-Cherng Liang\, Nicolas Gisin\, A tri
 partite quantum state violating the hidden influence constraints\, quant-p
 h/1304.1812\, PRA in press.\n \n
LOCATION:Seminar Room 1\, Newton Institute
END:VEVENT
END:VCALENDAR