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SUMMARY:Measurement in quantum field theory - Professor Chris Fewster - Yo
 rk
DTSTART:20251022T150000Z
DTEND:20251022T160000Z
UID:TALK238042@talks.cam.ac.uk
CONTACT:Amanda Stagg
DESCRIPTION:Many presentations of quantum mechanics include a postulate th
 at the state of a system undergoes an instantaneous change following a mea
 surement. This is clearly incompatible with special and general relativity
  and raises questions concerning the description of measurement in quantum
  field theory (QFT).\n\nAttempts to extend measurement postulates to QFT b
 y hand have produced pathologies\, such as the "impossible measurements" d
 escribed long ago by Sorkin.\n\nI will present a recent operational approa
 ch to these questions\, which models measurement of one quantum field (the
  system) by coupling it to another (the probe). This is all accomplished i
 n a model-independent way within algebraic quantum field theory (AQFT). Th
 e resulting framework provides a description of measurement in QFT that is
  causal\, covariant and consistent\, and includes state update rules that 
 are derived from the formalism\, and works equally well in flat or curved 
 spacetimes. As well as covering the basics of the formalism and how it res
 olves Sorkin's impossible measurement problem\, I will touch on some more 
 recent developments\, including links to quantum reference frames. \n\nI w
 ill not assume any prior knowledge of AQFT.\n\nThe talk is mostly based on
  joint work with Rainer Verch (Comm. Math. Phys. 378 (2020) 851-889 arXiv:
 1810.06512) and further work with Henning Bostelmann\, Maximilian Ruep and
  Ian Jubb (see https://arxiv.org/abs/2304.13356 for a survey). I will also
  mention recent joint work with Daan Janssen\, Leon Loveridge\, Kasia Rejz
 ner\, James Waldron (Comm. Math. Phys. 406:19 (2025)   https://arxiv.org/a
 bs/2403.11973)\n
LOCATION:MR3
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