The paper shows that for some pairs of unitary channels, perfect discrimination is possible with separable states but nearly impossible with maximally entangled states, introducing MEWC and MEBC concepts.
Conditions for optimal input states for discrimination of quantum channels
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abstract
We find optimality conditions for testers in discrimination of quantum channels. These conditions are obtained using semidefinite programming and are similar to optimality conditions for POVMs obtained by Holevo for ensembles of quantum states. We get a simple condition for existence of an optimal tester with any given input state with maximal Schmidt rank, in particular with a maximally entangled input state and we show the pitfalls of using input states with not maximal Schmidt rank. In case when maximally entangled state is not the optimal input state an error estimate is obtained. The results for maximally entangled input state are applied to covariant channels, qubit channels, unitary channels and simple projective measurements.
fields
quant-ph 1years
2026 1verdicts
UNVERDICTED 1representative citing papers
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Entanglement in quantum channel discrimination: sometimes less is more
The paper shows that for some pairs of unitary channels, perfect discrimination is possible with separable states but nearly impossible with maximally entangled states, introducing MEWC and MEBC concepts.