Estimation of quantum finite mixtures

J. I. de Vicente, J. Calsamiglia, R. Muñoz-Tapia, and E. Bagan
Phys. Rev. A 81, 012332 – Published 29 January 2010

Abstract

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.

  • Received 8 October 2009

DOI:https://doi.org/10.1103/PhysRevA.81.012332

©2010 American Physical Society

Authors & Affiliations

J. I. de Vicente, J. Calsamiglia, R. Muñoz-Tapia, and E. Bagan

  • Grup de Física Teòrica, Facultat de Ciències, Edifici Cn, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona, Spain

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Vol. 81, Iss. 1 — January 2010

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