Quantum phase noise reduction in soliton collisions and application to nondemolition measurements

We show that soliton collisions can reduce propagation-induced quantum phase noise. This effect originates from a negative correlation between self- and cross-phase-modulation-induced phase fluctuations. Furthermore, we show how this effect can be applied directly to improve the quality of soliton-based quantum nondemolition measurements, simply by adjusting the parameter regime in which the measurement is performed. Optimal implementation, which we show to be technologically feasible, favors short propagation distances, small wavelength separation between solitons, and approximately equal soliton amplitudes.