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