Collective versus local measurements in a qubit mixed-state estimation
Bagán Capella, Emili (Universitat Autònoma de Barcelona. Departament de Física)
Baig i Aleu, Marià, 1955- (Universitat Autònoma de Barcelona. Departament de Física)
Muñoz Tapia, Ramon (Universitat Autònoma de Barcelona. Departament de Física)
Rodríguez González, Alberto (Universidad de Salamanca. Area de Física Teórica)
American Physical Society

Date:	2004
Abstract:	We discuss the problem of estimating a qubit mixed state. We give the optimal estimation that can be inferred from any given set of measurements. For collective measurements and for a large number N of copies, we show that the error in the estimation varies as 1/N. For local measurements, we focus on the simpler case of states lying on the equatorial plane of the Bloch sphere. We show that the error using plain tomography varies as 1/N1/4, while our approach leads to an error proportional to 1/N3/4.
Rights:	Tots els drets reservats.
Language:	Anglès
Document:	Article ; recerca ; Versió publicada
Published in:	Physical review. A, Vol. 69, Issue 1 (January 2004) , p. 010304-1-010304-4, ISSN 1050-2947

DOI: 10.1103/PhysRevA.69.010304

4 p, 62.4 KB

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