Logical pre- and post-selection paradoxes are proofs of contextuality

Matthew F. Pusey, Matthew S. Leifer

Research output: Chapter in Book/Report/Conference proceedingConference contribution


If a quantum system is prepared and later post-selected in certain states, "paradoxical" predictions for intermediate measurements can be obtained. This is the case both when the intermediate measurement is strong, i.e. a projective measurement with Luders-von Neumann update rule, or with weak measurements where they show up in anomalous weak values. Leifer and Spekkens [quant-ph/0412178] identified a striking class of such paradoxes, known as logical pre- and post-selection paradoxes, and showed that they are indirectly connected with contextuality. By analysing the measurement-disturbance required in models of these phenomena, we find that the strong measurement version of logical pre- and post-selection paradoxes actually constitute a direct manifestation of quantum contextuality. The proof hinges on under-appreciated features of the paradoxes. In particular, we show by example that it is not possible to prove contextuality without Luders-von Neumann updates for the intermediate measurements, nonorthogonal pre- and post-selection, and 0/1 probabilities for the intermediate measurements. Since one of us has recently shown that anomalous weak values are also a direct manifestation of contextuality [arXiv:1409.1535], we now know that this is true for both realizations of logical pre- and post-selection paradoxes.
Original languageEnglish
Title of host publicationProceedings of the 12th International Workshop on Quantum Physics and Logic
EditorsChris Heunen, Peter Selinger, Jamie Vicary
Number of pages12
Publication statusPublished - 5 Nov 2015

Publication series

NameElectronic Proceedings in Theoretical Computer Science
ISSN (Electronic)2075-2180

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