In the past, I thought I have seen quantum circuits/algorithm techniques to change the amplitude of state based on the state?
$\lvert \psi \rangle = \sum_x \ C_x \lvert x \rangle$, here $C_x$ is just constant (i.e. as in simple superpositions)
and after some $U$, $\lvert \psi \rangle = \sum_x \ C_x (x) \lvert x \rangle$
The amplitude changes based on the $\lvert x \rangle$ state.
Any pointer or reference would be appreciated.