Collective versus local measurements in a qubit mixed-state estimation

E. Bagan, M. Baig, R. Muñoz-Tapia, A. Rodriguez

Research output: Contribution to journalArticleResearchpeer-review

35 Citations (Scopus)


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 [Formula Presented] 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 [Formula Presented] while our approach leads to an error proportional to [Formula Presented]. © 2004 The American Physical Society.
Original languageEnglish
Article number010304
Pages (from-to)103041-103044
JournalPhysical Review A - Atomic, Molecular, and Optical Physics
Issue number1
Publication statusPublished - 1 Jan 2004


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