= Nonselective quantum measurement
{title2=$\rho'=\sum_iA_i\rho A_i^\dagger$}
A nonselective <quantum measurement> averages over outcomes that are not read or not communicated. Its <quantum channel> is $\rho\mapsto\sum_iA_i\rho A_i^\dagger$, with $\sum_iA_i^\dagger A_i=I$. The completeness condition makes the channel trace preserving. The average equals $\sum_i p_i\rho_i$, where $\rho_i$ are the conditional states from a <selective quantum measurement>. A <nonselective projective measurement> is the special case in which the operators are orthogonal projectors.
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