= Measurement direction of a CNOT interaction
{title2=$U=I_S\otimes Q_++Z_S\otimes Q_-$}
A <CNOT gate> can correlate either the original control's computational label with a computational pointer, or the original target's sign-basis label with a sign-basis pointer. For the second interpretation prepare the original control in $|+\rangle$ and read it in the <Hadamard basis>. Its two pointer states become $|+\rangle$ and $|-\rangle$, measuring $X$ on the original target. An apparatus role therefore depends on the ready state and readout as well as the <measurement interaction>.
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