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Quantum Engineering Grenoble Seminar || Quantum Foundations - Hippolyte Dourdent

on the February 11, 2020

at 10:30.
Witness of Quantum Weirdness Contextuality is certainly one of the most fundamental aspects of quantum weirdness. In fact, it is usually said that “in quantum mechanics, the result of a measurement depends on the experimental context”. This statement - often vaguely attributed to Bohr- finds a concrete foundation in a theorem established by Ernst Specker and Simon Kochen (1960-1967) and John Bell (1964-1966). This presentation aims at introducing their result and highlights why it is a key feature to understanding the core of what makes quantum mechanics “weird”.
In this second talk, I will (re)introduce the Kochen-Specker theorem by giving simple proofs based on coloring. I will then present how quantum non-locality can be understood as a special case of contextuality via the case study of a famous paradox by Hardy [5]. In turn, this analysis will allow me to introduce a recent paradox by Frauchiger and Renner [6]. I will discuss their polemical statement - ``Quantum theory cannot consistently describe the use of itself.’’ - in the light of the analogy between quantum contextuality and famous paradoxes in classical logics [7]. 
 
[1] H. Dourdent, “Contextuality, Witness of Quantum Weirdness”, arXiv:180109768 [quant-ph], 2018 (in French)
[2] E. Specker, “Die Logik Nicht Gleichzeitig Entscheidbarer Aussagen,” Dialectica, 1960 
[3] S. Kochen and E. Specker, “The Problem of Hidden Variables in Quantum Mechanics,” Journal of Mathematics and Mechanics, vol. 17, 1967
[4] J. S. Bell, “On the Problem of Hidden Variables in Quantum Mechanics,” Rev. Mod. Phys., vol. 38, 1966 
[5] L. Hardy, “Nonlocality for two particles without inequalities for almost all entangled states,” Phys. Rev. Lett., vol. 71, 1993.
[6] D. Frauchiger and R. Renner, “Quantum theory cannot consistently describe the use of itself,” Nature Communications, vol. 9, 2018.
[7] S. Abramsky, S. Mansfield, and R. S. Barbosa, “The Cohomology of Non-Locality and Contextuality,” QPL 2011.
 
(The talk is aimed at a large audience; basic knowledge in quantum theory will be sufficient to follow it.)

Come along and feel free to forward this information.
If you need an authorisation to enter the CNRS campus, please contact Cyril Branciard (cyril.branciard@neel.cnrs.fr).
 
Published on February 7, 2020

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In room K-223 of the Institut Néel.