Quantum images in nonlinear optics

We illustrate the concept of quantum image in the context of degenerate parametric oscillators. In the case of a cavity with planar mirrors, we show the gradual transformation of a quantum image into a classical image as the threshold region is scanned. Thus the quantum image behaves as a precursor of the roll pattern which appears above threshold. In the far field, the configuration of the spatial correlation function of the intensity and of the quadrature components shows unambiguously the quantum nature of fluctuations that generate the quantum image, leading to effects of quantum noise reduction below the shot noise level, and to the formulation of an Einstein–Podolsky–Rosen paradox.