Assume that a preparation apparatus does not work completely accurately and prepares systems with states ϕ1, ϕ2, ϕ3 …, say, with a priori probabilities p1, p2, p3 …, which depend on the construction of the apparatus. In this case, any 390 Mixing and Oscillations of Particles single system is actually in one of the states ϕi, which one, however, is not known to the observer who knows only the probabilities. This very special kind of a mixed stated is called a “mixture of states” [2], or “real mixture” [3] or a “Gemenge” [4]. A “Gemenge” ΓS (pk, ϕk) is a classicalmixture of states ϕk with weights pk.
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Literature
J. M. Jauch: Foundations of Quantum Mechanics (Addison-Wesley, Reading, MA, 1968, 96)
P. Mittelstaedt: The Interpretation of Quantum Mechanics and the Measurement Process (Cambridge University Press, Cambridge, 1998, 35–37)
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Mittelstaedt, P. (2009). Mixed State. In: Greenberger, D., Hentschel, K., Weinert, F. (eds) Compendium of Quantum Physics. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-70626-7_120
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