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"Partial" Fidelities

Armin Uhlmann

quant-pharXiv:quant-ph/9912114

Abstract

For pairs, omega, rho, of density operators on a finite dimensional Hilbert space of dimension d I call k-fidelity the d - k smallest eigenvalues of | omega1/2 rho1/2 |. k-fidelities are jointly concave in omega, rho. This follows by representing them as infima over linear functions. For k = 0 known properties of fidelity and transition probability are reproduced. Partial fidelities characterize equivalence classes which are partially ordered in a natural way.

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