Abstract

In a shot-noise-limited (coherent state) phasesensing interferometer, the root-mean-square (rms) phase error is $~1/N_{\text{av}}^{1/2}$ where N_av is the average number of detected photons. In an optimized squeezed-state interferometer, the rms phase error goes as 1/N_av. We have considered the phase measurement problem from the viewpoint of quantum estimation theory.¹ In particular, for the problem of optimum phase-shift estimation from observation of a single mode of the radiation field under an average photon number constraint, we have found both the optimum quantum state and the optimum quantum measurement. The former turns out to have a truncated number-state expansion whose coefficients, out to the truncation point, fall off as 1/n. The latter turns out to be the Susskind-Glogower phase operator. More important, the resulting phase estimation performance improves as $1/N_{\text{av}}^2$.

© 1988 Optical Society of America