Optimal quantum circuits for general phase estimation.
We address the problem of estimating the phase phi given N copies of the phase-rotation gate uphi. 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 phi for phi depends only on the difference phi-phi, 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.
van Dam
Wim
W
Departments of Computer Science and Physics, University of California, Santa Barbara, Santa Barbara, California 93106-5110, USA.
D'Ariano
G Mauro
GM
Ekert
Artur
A
Macchiavello
Chiara
C
Mosca
Michele
M