Purity Estimation with Separable Measurements

TitlePurity Estimation with Separable Measurements
Publication TypeJournal Article
Year of Publication2005
AuthorsBagan, E, Ballester, MA, Muñoz-Tapia, R, Romero-Isart, O
JournalPhysical Review Letters
Volume95
Issue11
Pagination110504
Date Published09/2005
ISSN0031-9007
Abstract

Given a large number N of copies of a qubit state of which we wish to estimate its purity, we prove that separable-measurement protocols can be as efficient as the optimal joint-measurement one if classical communication is used. This shows that the optimal estimation of the entanglement of a two-qubit state can also be achieved asymptotically with fully separable measurements. Thus, quantum memories provide no advantage in this situation. The relationship between our global Bayesian approach and the quantum Cramér-Rao bound is discussed.

URLhttp://link.aps.org/doi/10.1103/PhysRevLett.95.110504
DOI10.1103/PhysRevLett.95.110504
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