Optimal quantum circuits for general phase estimation

Abstract

We address the problem of estimating the phase given N copies of the phase-rotation gate u. We consider, for the first time, the optimization of the general case where the circuit consists of an arbitrary input state, followed by any arrangement of the N phase rotations interspersed with arbitrary quantum operations, and ending with a general measurement. Using the polynomial method, we show that, in all cases where the measure of quality of the estimate for depends only on the difference -, the optimal scheme has a very simple fixed form. This implies that an optimal general phase estimation procedure can be found by just optimizing the amplitudes of the initial state. © 2007 The American Physical Society.