= Quantum premeasurement
The coherent interaction that correlates a system observable with detector records before selecting an outcome. An ideal coupling maps $|s_j\rangle|d_0\rangle$ to $|s_j\rangle|d_j\rangle$. Linearity then maps a superposition to $\sum_j c_j|s_jd_j\rangle$. The full state can remain pure and entangled, whereas a nonselective <projective measurement> removes coherence between different record sectors. Conditioning on one observed record is a third, selective operation.
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