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SUMMARY:Leggett Garg Inequalities: a Quasi-probability Approach to No-Sign
 alling in Time and New Measurement Protocols - Jonathan Halliwell\, Imperi
 al
DTSTART:20170126T141500Z
DTEND:20170126T151500Z
UID:TALK69510@talks.cam.ac.uk
CONTACT:Steve Brierley
DESCRIPTION:The Leggett-Garg (LG) inequalities were proposed in order to a
 ssess whether sets of pairs of sequential measurements on a single quantum
  system can be consistent with an underlying notion of macroscopic realism
  (MR) at three\, four or more times. I review the LG formalism and note th
 at the LG inequalities alone are a necessary condition for MR\, but not a 
 sufficient one\, the shortfall lying in the description of the system at t
 wo times\, the key point at which LG systems differ from the analogous CHS
 H inequalities for an EPRB pair. I argue that this shortfall can be addres
 sed by describing the two-time measurement situation in terms of a simple\
 , measurable quasi-probability\, which provides a measure of macrorealism 
 at two times. It is closely related to the no-signalling in time condition
  of Kofler and Brukner. This measure\, when combined with the LG inequalit
 ies\, provides a characterization of macrorealism more detailed than that 
 provided by the LG inequalities alone. In particular\, when the quasi-prob
 ability is non-negative\, the LG system has a natural parallel with the EP
 RB system and Fine’s theorem\, and this augmented LG system is then both
  a necessary and sufficient condition for macrorealism. In all experiments
  measuring such systems\, the measurements have to be carried out non-inva
 sively in order to evade alternative classical explanations. Two simple pr
 otocols are proposed to achieve this.\n\nThe Leggett-Garg Inequalities and
  No-Signalling in Time: A Quasi-Probability Approach. J. J. Halliwell Phys
 . Rev. A 93\, 022123 (2016)\n\nDecoherent Histories and Measurement of Tem
 poral Correlation Functions for Leggett-Garg Inequalities. J.J.Halliwell P
 hys. Rev. A 94\, 052131 (2016)\n\nLeggett-Garg Correlation Functions from 
 Non-Invasive Velocity Measurement Continuous in Time. J.J. Halliwell Phys.
  Rev. A 94\, 052114 (2016)
LOCATION:MR4\, Centre for Mathematical Sciences\, Wilberforce Road\, Cambr
 idge
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