Collective versus local measurements in a qubit mixed-state estimation

TitleCollective versus local measurements in a qubit mixed-state estimation
Publication TypeJournal Article
Year of Publication2004
AuthorsBagan, E, Baig, M, Muñoz-Tapia, R, Rodriguez, A
JournalPhysical Review A (Atomic, Molecular, and Optical Physics)
Volume69
Issue1
Pagination010304
Date Published01/2004
ISSN1050-2947
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.

URLhttp://link.aps.org/doi/10.1103/PhysRevA.69.010304
DOI10.1103/PhysRevA.69.010304
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