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arXiv:quant-ph/0401112 · Physical Review A

Proposed direct test of a certain type of noncontextuality in quantum mechanics

Karl Svozil

Published Oct 9, 2009• 20 citations
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Abstract

The noncontextuality of quantum mechanics can be directly tested by measuring two entangled particles with more than two outcomes per particle. The two associated contexts are ``interlinked'' by common observables.
DOI
10.1103/physreva.80.040102

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Two entangled particles in threedimensional Hilbert space (per particle) are considered in an EPR-type arrangement. On each side the Kochen-Specker observables {J12,J22,J32}\{J_1^2,J_2^2,J_3^2\}{J12​,J22​,J32​} and {Jˉ12,Jˉ22,J32}\{\bar J_1^2, \bar J_2^2,J_3^2\}{Jˉ12​,Jˉ22​,J32​} with [J12,Jˉ12]≠0[J_1^2,\bar J_1^2]\neq 0[J12​,Jˉ12​]=0 are measured. The outcomes of measurements of J32J_3^2J32​ (via J12,J22J_1^2,J_2^2J12​,J22​) and J32J_3^2J32​ (via Jˉ12,Jˉ22\bar J_1^2,\bar J_2^2Jˉ12​,Jˉ22​) are compared. Although formally J32J_3^2J32​ is associated with the same projection operator, a strong form of quantum contextuality states that an outcome depends on the complete disposition of the measurement apparatus, in particular whether J12J_1^2J12​ or Jˉ12\bar J_1^2Jˉ12​ is measured alongside. It is argued that in this case it is impossible to measure contextuality directly, a necessary condition being a non-operational counterfactuality of the argument.
The Klyachko inequality is an inequality for the probabiities of the values of five observables of a spin-1 particle, which is satisfied by any noncontextual assignment of values to this set of observables, but is violated by the probabilities defined by a certain quantum state. We describe an experiment between two entangled spin-1 particles to test contextuality via a related inequality. We point out that a test of contextuality by measurements on a single particle to confirm the Klyachko inequality requires an assumption of non-disturbance by the measuring instrument, which is avoided in the two-particle experiment.