Experimental demonstration of phase measurement precision beating shot noise limit

摘要

We propose an experimental scheme to show the precision of the phase measurement approach the Heisenberg limit with photon pairs from parametric downconversion. The initial multi-photon state is the twin fock state with equal photon number which have been argued by Holland and Burnett [Phys.Rev. Lett. 71, 1355 (1993)]. However, the measurement is the two-mode multi-photon state projection measurement which can be conveniently realized with linear optical elements. Compared with the Heisenberg limit 1/N, the precision of this scheme is about 1.4/N when the photon number N is much larger than 1. Moreover, we perform the experiment on the few photons state and obtain the phase uncertainty of 0.526 for two-photon state and 0.299 for four-photon state, which is much better than the shot noise limit.