Quantum channel discrimination
= Quantum channel discrimination
{wiki}
Quantum channel discrimination feeds a common input into one of several candidate <quantum channels> and measures the output. An entangled <quantum ancilla> permits inputs $\rho_{HR}$ and compares $(T_j\otimes\operatorname{id}_R)(\rho_{HR})$; optimal binary discrimination is governed by the <diamond norm> of the weighted channel difference.