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Advances in Mathematical Physics
Volume 2010, Article ID 945460, 11 pages
Review Article

Two Versions of the Projection Postulate: From EPR Argument to One-Way Quantum Computing and Teleportation

School of Mathematics and Systems Engineering, International Center of Mathematical Modeling in Physics and Cognitive Sciences, Växjö University, 35195, Sweden

Received 17 August 2009; Accepted 29 December 2009

Academic Editor: Shao-Ming Fei

Copyright © 2010 Andrei Khrennikov. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Nowadays it is practically forgotten that for observables with degenerate spectra the original von Neumann projection postulate differs crucially from the version of the projection postulate which was later formalized by Lüders. The latter (and not that due to von Neumann) plays the crucial role in the basic constructions of quantum information theory. We start this paper with the presentation of the notions related to the projection postulate. Then we remind that the argument of Einstein-Podolsky-Rosen against completeness of QM was based on the version of the projection postulate which is nowadays called Lüders postulate. Then we recall that all basic measurements on composite systems are represented by observables with degenerate spectra. This implies that the difference in the formulation of the projection postulate (due to von Neumann and Lüders) should be taken into account seriously in the analysis of the basic constructions of quantum information theory. This paper is a review devoted to such an analysis.