Quantum research reveals when entanglement hinders rather than helps channel discrimination

Entanglement is known to be a powerful resource that improves performance in various quantum information and computational tasks.

While entanglement is often a powerful resource for quantum channel discrimination, this is not necessarily the case.

In this work, we identify scenarios in which the maximally entangled state is a bad choice of input state and, more generally, show that excessive entanglement can reduce channel discriminability dramatically.

We present an explicit pair of unitary channels which are perfectly discriminable without entanglement, but for which any strategy with maximally entangled input states is ε-close to a blind uniform guessing strategy.

We show that the optimal input states for discriminating MEWC pairs of channels are necessarily separable, and provide non-trivial examples of measurement channels for which entanglement necessarily reduces the maximum probability of discrimination.