For lower values of the pump there is a convectively unstable regime in which intensity patterns sustained by noise are observed for each polarization. This patterns arise from the interference among traveling waves that are generated by the dynamical amplification of noise. These issues have been studied in OPOs, Kerr cavities, and in cavityless configurations for quadratic and cubic nonlinear media. However, in general , the vectorial character of the light has not been taken into account, despite the fact that in many cases it originates a much richer scenario of pattern forming instabilities. On the left box, the upper figure shows a diagram of the Kerr cavity.
Pin is the input pump field .
We have shown the existence of anti-correlations between the quantum flutuations of the pump and the sum of intensities of M1 and M2. We have shown that in the self-defocusing case, where a vectorial pattern is formed it is possible to perform a Quantum Nondemolition measurement of the intensity fluctuations of the pump by using the fluctuations of M1 and M2 as meter . For the scalar pattern formed in the self-focusing case such a measurement does not fulfill the necessary conditions to be of nondemolition nature. R. Zambrini et al. M. Hoyuelos, A. Gatti, P. Colet and M. San Miguel, Quantum Optics X, Physical Review October 1999.