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CATEGORIES:CQIF Seminar
SUMMARY:Leggett Garg Inequalities: a Quasi-probability App
roach to No-Signalling in Time and New Measurement
Protocols - Jonathan Halliwell\, Imperial
DTSTART;TZID=Europe/London:20170126T141500
DTEND;TZID=Europe/London:20170126T151500
UID:TALK69510AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/69510
DESCRIPTION:The Leggett-Garg (LG) inequalities were proposed i
n order to assess whether sets of pairs of sequent
ial measurements on a single quantum system can be
consistent with an underlying notion of macroscop
ic realism (MR) at three\, four or more times. I r
eview the LG formalism and note that the LG inequa
lities alone are a necessary condition for MR\, bu
t not a sufficient one\, the shortfall lying in th
e description of the system at two times\, the key
point at which LG systems differ from the analogo
us CHSH inequalities for an EPRB pair. I argue tha
t this shortfall can be addressed by describing th
e two-time measurement situation in terms of a sim
ple\, measurable quasi-probability\, which provide
s a measure of macrorealism at two times. It is cl
osely related to the no-signalling in time conditi
on of Kofler and Brukner. This measure\, when comb
ined with the LG inequalities\, provides a charact
erization of macrorealism more detailed than that
provided by the LG inequalities alone. In particul
ar\, when the quasi-probability is non-negative\,
the LG system has a natural parallel with the EPRB
system and Fine’s theorem\, and this augmented LG
system is then both a necessary and sufficient co
ndition for macrorealism. In all experiments measu
ring such systems\, the measurements have to be ca
rried out non-invasively in order to evade alterna
tive classical explanations. Two simple protocols
are proposed to achieve this.\n\nThe Leggett-Garg
Inequalities and No-Signalling in Time: A Quasi-Pr
obability Approach. J. J. Halliwell Phys. Rev. A 9
3\, 022123 (2016)\n\nDecoherent Histories and Meas
urement of Temporal Correlation Functions for Legg
ett-Garg Inequalities. J.J.Halliwell Phys. Rev. A
94\, 052131 (2016)\n\nLeggett-Garg Correlation Fun
ctions from Non-Invasive Velocity Measurement Cont
inuous in Time. J.J. Halliwell Phys. Rev. A 94\, 0
52114 (2016)
LOCATION:MR4\, Centre for Mathematical Sciences\, Wilberfor
ce Road\, Cambridge
CONTACT:Steve Brierley
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