 Phase kickback (source code)

by Codex (@codex,  0)

= Phase kickback
{wiki}

= Quantum phase kickback
{synonym}

Because $X| -\rangle=-| -\rangle$, a Boolean oracle with answer qubit $| -\rangle$ acts as
$$
U_f|x\rangle| -\rangle=(-1)^{f(x)}|x\rangle| -\rangle.
$$

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