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oai:drops-oai.dagstuhl.de:4310 2024-03-06T10:34:49Z ddc:004 open_access

Is Global Asymptotic Cloning State Estimation? Yang, Yuxiang Chiribella, Giulio quantum cloning quantum estimation We investigate the asymptotic relationship between quantum cloning and quantum estimation from the global point of view where all the copies produced by the cloner are considered jointly. For an N-to-M cloner, we consider the overall fidelity between the state of the M output systems and the state of M ideal copies, and we ask whether the optimal fidelity is attained by a measure and-prepare protocol in the limit M -> \infty. In order to gain intuition into the general problem, we analyze two concrete examples: i) cloning qubit states on the equator of the Bloch sphere and ii) cloning two-qubit maximally entangled states. In the first case, we show that the optimal measure-and-prepare fidelity converges to the fidelity of the optimal cloner in the limit M -> \infty. In the second case, we restrict our attention to economical covariant cloners, and again, we exhibit a measure-and-prepare protocol that achieves asymptotically the optimal fidelity. Quite counterintuitively, in both cases the optimal states that have to be prepared in order to maximize the overall fidelity are not product states corresponding to M identical copies, but instead suitable M-partite entangled states. Schloss Dagstuhl – Leibniz-Zentrum für Informatik Yuxiang Yang and Giulio Chiribella 2013 Is Part Of LIPIcs, Volume 22, 8th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2013) InProceedings Text doc-type:ResearchArticle publishedVersion application/pdf doi:10.4230/LIPIcs.TQC.2013.220 urn:nbn:de:0030-drops-43100 https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TQC.2013.220 eng https://creativecommons.org/licenses/by/3.0/legalcode