Purity estimation with separable measurements

E. Bagan, M. A. Ballester, R. Muñoz-Tapia, O. Romero-Isart

Research output: Contribution to journalArticleResearchpeer-review

21 Citations (Scopus)


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. © 2005 The American Physical Society.
Original languageEnglish
Article number110504
JournalPhysical Review Letters
Publication statusPublished - 9 Sep 2005


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