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SUMMARY:The measurement postulates are redundant - Lluis Masanes\, London 
 Centre for Nanotechnology\, University College London
DTSTART:20220120T141500Z
DTEND:20220120T151500Z
UID:TALK168023@talks.cam.ac.uk
CONTACT:Damian Pitalua-Garcia
DESCRIPTION:The measurement postulates specify: the mathematical structure
  of quantum measurements (Hermitian operators\, POVMs)\, the formula for a
 ssigning outcome probabilities (Born’s rule) and the post-measurement st
 ate-update rule. The rest of postulates are often referred to as “unitar
 y quantum mechanics”. We characterise the family of theories consisting 
 of unitary quantum mechanics supplemented with non-quantum measurement pos
 tulates\; and prove that any such theory has the following problematic fea
 ture: the set of mixed state of any finite-dimensional Hilbert space has i
 nfinite dimension\, which makes the task of state estimation impossible. T
 herefore\, if we disregard theories with this problematic feature then the
  only measurement postulates compatible with unitary quantum mechanics are
  the good old quantum measurement postulates. This result reveals the true
  identity of the “measurement postulates” as “measurement theorems
 ”.
LOCATION:MR2 Centre for Mathematical Sciences
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