Quantum-nondemolition criteria in traveling-wave second-harmonic generation - art. no. 023802

Using the full nonlinear equations of motion, we calculate the quantum-nond emolition (QND) correlations for the traveling-wave second-harmonic generat ion. We find that, after a short interaction length, these are qualitativel y different from results calculated previously using a linearized fluctuati on analysis. We demonstrate that, although individual QND criteria can be v ery good in certain regions, there is no region when all three of the stand ard criteria are perfect, as has previously been claimed. We also show that only the amplitude quadrature of the output field can be considered as a Q ND quantity, with the phase quadrature not satisfying all the criteria.