Estimation of quantum finite mixtures
de Vicente Majúa, Julio Íñigo (Universitat Autònoma de Barcelona. Departament de Física)
Calsamiglia Costa, John (Universitat Autònoma de Barcelona. Departament de Física)
Muñoz Tapia, Ramon (Universitat Autònoma de Barcelona. Departament de Física)
Bagán Capella, Emili (Universitat Autònoma de Barcelona. Departament de Física)
American Physical Society

Data:	2010
Resum:	We consider the problem of determining the weights of a quantum ensemble. That is to say, given a quantum system that is in a set of possible known states according to an unknown probability law, we give strategies to estimate the individual probabilities, weights, or mixing proportions. Such strategies can be used to estimate the frequencies at which different independent signals are emitted by a source. They can also be used to estimate the weights of particular terms in a canonical decomposition of a quantum channel. The quality of these strategies is quantified by a covariance-type error matrix. According with this cost function, we give optimal strategies in both the single-shot and multiple-copy scenarios. The latter is also analyzed in the asymptotic limit of large number of copies. We give closed expressions of the error matrix for two-component quantum mixtures of qubit systems. The Fisher information plays an unusual role in the problem at hand, providing exact expressions of the minimum covariance matrix for any number of copies.
Drets:	Tots els drets reservats.
Llengua:	Anglès
Document:	Article ; recerca ; Versió publicada
Publicat a:	Physical review. A, Vol. 81, Issue 1 (January 2010) , p. 012332-1-012332-12, ISSN 1050-2947

DOI: 10.1103/PhysRevA.81.012332

12 p, 253.3 KB

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