Quantum correlations close to a square pattern forming instability

Abstract

We analyze the quantum fluctuations of the degenerate optical parametric oscillator close to an instability for the formation of a square pattern. While strong correlations between the fluctuations of the signal modes emitted at the critical wave number and with opposite wave vector are present both below and above threshold, no features signaling the square character of the pattern forming above threshold have been identified below threshold in the spatio-temporal second-order coherence. We also explore in which regimes a reduced few mode model gives meaningful results.