Ballesteros, M.; Fraas, M.; Fröhlich, J.; Schubnel, B.
(2016):
Indirect Acquisition of Information in Quantum Mechanics.
In: Journal of Statistical Physics, Vol. 162, No. 4: pp. 924958

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Abstract
Long sequences of successive direct (projective) measurements or observations of just a few "uninteresting" physical quantities pertaining to a quantum system, such as clicks of some detectors, may reveal indirect, but precise and unambiguous information on the values of some very "interesting" observables of the system. In this paper, the mathematics underlying this claim is developed;i. e., we attempt to contribute to a mathematical theory of indirect and, in particular, nondemolition observations and measurements in quantum mechanics. Our attempt leads us to make some novel uses of classical notions and results of probability theory, such as the "algebra of functions measurable at infinity", the Central Limit Theorem, results concerning relative entropy and its role in the theory of large deviations, etc.