Quantum contextuality is one of the most intriguing phenomenon related to the foundational issues of quantum theory. According to it the measurement result of an observable depends on the arrangements made to measure it. Arrangement here means that the type of commuting observable being measured along (previous or simultaneous) with it. The result of measurement is different when an observable is measured with a different commuting observable.
Andrew Gleason was the one who proposed a theorem showing for the first time that contextuality exists only in dimensions which is greater than two. Of course it was first of all pointed out by Niels Bohr in his paper which says that EPR-like paradoxes occur in the quantum systems without the need for an entangled or composite systems.
Kochen and Specker
- Gleason, A. M, "Measures on the closed subspaces of a Hilbert space", Journal of Mathematics and Mechanics 6, 885–893 (1957).
- N. Bohr, "Can Quantum-Mechanical Description of Physical Reality be Considered Complete?", Phys. Rev. 48, 696–702 (1935).
- S. Kochen and E.P. Specker, "The problem of hidden variables in quantum mechanics", Journal of Mathematics and Mechanics 17, 59–87 (1967).