We present the measurement of entanglement between twin beams generated with a doubly resonant optical parameter oscillator (OPO) based on four-wave mixing in hot 85 Rb vapor above threshold. This is the first measurement of entanglement in an OPO with χ (3) media above threshold. We reconstruct the covariance matrix for several configurations and with a full picture of the four side band mode state, we study entanglement between all possible bi-partitions. We show a robust generation of entanglement with stronger generation for a specific pair of modes. For this system, we show that atomic density is a determinant factor for generation and loss of quantum correlations. The generation of entangled fields by an atomic OPO close to atomic resonance of alkali atoms enables natural integration into quantum networks.

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We present a microscopic description of dressed four wave mixing (4WM) demonstrating spectral control of quantum correlations. Starting from a double Λ model for a single pump 4WM, we include a dressing field coupling the excited level which leads to a six wave mixing process (6WM). The model describes the enhancement of the amplification and intensity difference squeezing due to the interaction of the dressing field, according to the experimental parameters. Moreover, the model predicts that this mechanism allows the spectral control of the quantum correlations between pair of side-bands by just tuning accordingly the dressing field.

We present a hidden entanglement between four-modes generated by stimulated FWM. Theoretically, we show the violation of DGCZ inequality for different sideband bipartitions. Experimentally we present previous results of the auto-homodyne detection and the asymmetry in the sidebands.