 von Neumann process 1

The projection step in the traditional measurement account. For outcome projectors $P_j$, the nonselective state is ${\sum }_j{P}_j\rho P_j$; conditional on outcome $j$ it is $P_j\rho P_j/\mathrm{Tr}(P_j\rho )$. Distinguishing these from the coherent state produced by quantum premeasurement avoids identifying a pure correlated projector with its dephased mixture.