Phys. Rev. A 70, 032321 (2004) [5 pages]Optimal measurements for relative quantum informationReceived 13 October 2003; published 23 September 2004 We provide optimal measurement schemes for estimating relative parameters of the quantum state of a pair of spin systems. We prove that the optimal measurements are joint measurements on the pair of systems, meaning that they cannot be achieved by local operations and classical communication. We also demonstrate that in the limit where one of the spins becomes macroscopic, our results reproduce those that are obtained by treating that spin as a classical reference direction. © 2004 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevA.70.032321
DOI:
10.1103/PhysRevA.70.032321
PACS:
03.67.Hk, 03.65.Ta, 03.65.Ud
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