NOISE-FREE QUANTUM-NONDEMOLITION MEASUREMENT USING OPTICAL SOLITONS

The collision of solitons in optical fibers is a promising scheme for the quantum-nondemolition measurement of the photon number using the c ross Kerr effect. In a realistic experimental situation, the sensitivi ty of the measurement is limited not only by self-phase-modulation noi se of the probe but also by the phase noise added due to the vibration al excitations of the fiber. Former schemes proposed to overcome eithe r of these problems are not compatible with each other. In this paper the sensitivity of different type of detection is carefully studied. W e propose a solution based on the use of a phase-shifting cavity. We s how that this provides a conceptually and practically simple solution eliminating simultaneously both sources of excess noise. [S1050-2947(9 8)04406-0].