Quantum-nondemolition schemes to measure quadrature phases using intracavity harmonic generation

In this paper, we present a theoretical investigation into the quantum-nondemolition (QND) properties of a system which utilizes intracavity harmonic generation. It is found that a nearly ideal QND measurement of the amplitude of a signal can be performed using second-harmonic generation, while subharmonic generation can be utilized to give a nearly ideal QND measurement of a phase. The results show a significant improvement over the QND properties of other systems studied previously and should be accessible to experiment.