= Quantum state exclusion
A task in which a <quantum measurement> outputs a label of a preparation that can be ruled out. If preparations are $\rho_j$ and the outcome labelled $j$ has effect $E_j$, error-free exclusion requires $\operatorname{Tr}(E_j\rho_j)=0$ for every $j$, together with $E_j\geq0$ and $\sum_jE_j=I$. A family admitting a complete error-free exclusion measurement consists of <antidistinguishable quantum states>. Exclusion need not identify the actual preparation.
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