Quantum phase estimation
= Quantum phase estimation
{wiki}
Given controlled powers of a unitary $U$ and an <eigenstate> $U|\psi\rangle=e^{2\pi i\phi}|\psi\rangle$, <quantum phase estimation> outputs an approximation to $\phi$. If the input is a superposition of <eigenstates>, measurement selects an eigenphase with <probability> equal to the squared magnitude of its coefficient.