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Optimal estimation of quantum dynamics

2001; American Physical Society; Volume: 64; Issue: 5 Linguagem: Inglês

10.1103/physreva.64.050302

1538-4446

Antonio Acín, E. Jané, Guifré Vidal,

Quantum Computing Algorithms and Architecture

We construct the optimal strategy for the estimation of an unknown unitary transformation $U\in SU(d)$. This includes, in addition to a convenient measurement on a probe system, finding which is the best initial state on which $U$ is to act. When $U\in SU(2)$, 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.