Hybrid correlation and squeezing with spontaneously generated coherence effect

We investigate intensity noise correlation of hybrid signals generated through spontaneous parametric four-wave mixing and fourth-order fluorescence signals from the nitrogen-vacancy center in diamond. The degree of hybrid correlation changes with power, frequency detuning, and experimental temperature. A theoretical model including spontaneously generated coherence in the dressed-state picture is set up to explain this phenomenon. We also observed damped Rabi oscillations in spontaneous parametric four-wave mixing and attributed it to quantum interference between two four-wave mixing transition paths.