Color defects in a diamond nitrogen-vacancy (NV) center represent an important physical system for emergent quantum technologies such as logic gates and registers at room temperature. Wei Zhao research team realized an optical logic NOT gate by inducing a phase shift in a diamond NV center under nonlinear Kerr effect of spontaneous parametric four-wave mixing (SP-FWM). Also, they discussed the intensity–noise correlation and intensity-difference squeezing of SP-FWM and composite signals (SP-FWM+fluorescence) under self-phase modulation (SPM) and cross-phase modulation (XPM) induced by the nonlinear Kerr effect in V-type and double V-type atomic systems. Their experimental results provide an advanced technique of switching contrast by approximately 90%. Different parameters, such as the power of input laser beam and boxcar gate position, were also configured to control the SPM and XPM, which determine the switching phenomenon for correlation and squeezing.

（Original research article "Journal of the Optical Society of America B Vol. 36, Issue 10, pp. 2727-2734 (2019). https://doi.org/10.1364/JOSAB.36.002727）