Three-field noise correlation via third-order nonlinear optical processes

We report experimental observation of three-field noise correlation between two coexisting four-wave mixing (FWM) signals and the probe signal in a coherently-prepared rubidium vapor system. The two FWM signals in a double-Λ type quasi-four-level atomic system are obtained in different directions via their respective phase-matching conditions and can be detected individually. These signals and the probe beam are found to be strongly correlated or anticorrelated with each other.