Purity and state fidelity of quantum channels
نویسندگان
چکیده
We associate with every quantum channel T acting on a Hilbert space H a pair of Hermitian operators, referred to as “Hamiltonians,” over the symmetric subspace of H^2. The expectation values of these Hamiltonians over symmetric product states give either the purity or the pure-state fidelity of T. This allows us to analytically compute these measures for a wide class of channels, and to identify states that are optimal with respect to these measures.
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