27 April 2009 Quantum Fisher information and the qudit depolarization channel
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Abstract
The quantum Fisher information is derived for the task of identifying the qudit depolarizing channel with any dimension. The identification scheme in which a pure state channel input is entangled with an ancilla system is shown to dominate other schemes for all qudit depolarizing channels of any dimension and any depolarizing rate. This extends known results for the qubit depolarizing channel. This dominance, though, is not robust; if the ancilla system itself undergoes any degree of depolarization, no matter how small, entanglement with the ancilla is no longer necessarily optimal. The quantum score operator for the qudit depolarizing channel has a special "quasi-classical" form, readily yielding these various results.
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Michael Frey, Michael Frey, David Collins, David Collins, } "Quantum Fisher information and the qudit depolarization channel", Proc. SPIE 7342, Quantum Information and Computation VII, 73420N (27 April 2009); doi: 10.1117/12.818668; https://doi.org/10.1117/12.818668
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