paper

Optimal estimation of quantum dynamics

arXiv:quant-ph/0012015 · doi:10.1103/PhysRevA.64.050302

Abstract

We construct the optimal strategy for the estimation of an unknown unitary transformation . This includes, in addition to a convenient measurement on a probe system, finding which is the best initial state on which is to act. When , such an optimal strategy can be applied to estimate simultaneously both the direction and the strength of a magnetic field, and shows how to use a spin 1/2 particle to transmit information about a whole coordinate system instead of only a direction in space.

4 pages, REVTEX

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