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SUMMARY:Aharonov meets Spekkens:  What do quantum paradoxes tell us about 
 the nature of reality?  - Matthew Leifer (Perimeter Institute)
DTSTART:20151015T131500Z
DTEND:20151015T141500Z
UID:TALK61128@talks.cam.ac.uk
CONTACT:William Matthews
DESCRIPTION:Over the last few decades\, Aharonov and collaborators have di
 scovered a large number of counterintuitive phenomena in quantum theory\, 
 such as the "three box paradox"\, the "quantum pigeonhole principle"\, "qu
 antum cheshire cats"\, and "protective measurement".  The interpretation o
 f these effects has always been controversial\, with ongoing arguments abo
 ut whether these effects have "classical" analogues as opposed to being "g
 enuinely quantum".\n\nIn this talk\, I will reanalyse these effects in lig
 ht of the work of Spekkens.  Spekkens emphasizes that many seemingly stran
 ge quantum phenomena actually have straightforward explanations if we view
  quantum states as states of incomplete knowledge about some underlying re
 ality.  Those that do not have such an explanation are the "genuinely quan
 tum" phenomena\, and these all seem to fall under the remit of Spekkens' g
 eneralized definition of contextuality.  So now we can make the question m
 ore precise: can Aharonov's phenomena be explained in theories in which th
 e quantum state represents incomplete knowledge and\, if not\, do they con
 stitute proofs of contextuality?\n\nI will show that a class of effects kn
 own as "logical pre- and post-selection paradoxes"\, which includes the th
 ree box paradox and the quantum pigeonhole principle\, do constitute direc
 t proofs of contextuality\, so they are "genuinely quantum" in Spekkens' s
 ense.  On the other hand\, protective measurement\, which was initially pr
 oposed as an argument for the reality of the quantum state\, is most easil
 y accounted for in theories in which the quantum state represents incomple
 te knowledge.\n\nThis talk is based on joint work with Josh Combes\, Chris
  Ferrie\, and Matt Pusey\, available in the papers arXiv:1506.07850 and  a
 rXiv:1509.08893
LOCATION:MR4\, Centre for Mathematical Sciences\, Wilberforce Road\, Cambr
 idge
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