Enhancing fluorescence of diamond NV⁻ centers for quantum sensing: A multi-layer optical antireflection coating

The negatively charged nitrogen-vacancy centers (NV⁻ centers) in diamonds possess outstanding magneto-optical properties and have broad applications in cutting-edge fields, such as quantum sensing, quantum communication, and quantum computing. However, the reflection loss around the wavelength of NV⁻ photoluminescence (PL) spectrum caused by the diamond–air interface is still a drawback. In this work, a multi-layer optical antireflection coating was designed via genetic algorithms to resolve this problem. The simulation results show that coating can increase the average transmissivity from 82.90 % to 99.84 %. We coated the diamond sample with eight SiO₂ and Ta₂O₅ overlapping layers based on the simulation results. After depositing the coating, the transmissivity increased from 83.84 % to 98.10 %, corresponding to a 17.01 % improvement. Furthermore, the intensity of the PL spectrum increased by a factor of 1.26, confirming the superior properties of the diamond–air interface with the coating. Finally, an NV-based magnetometer was constructed to prove the application significance of our coating. It was found that the sensitivity increased from 57.19 to 25.53 nT∙Hz^−1/2. This scheme demonstrates the positive effect of coating in improving the system's comprehensive performance, especially signal-to-noise ratio, but also benefits the miniaturization and integration of diamond magnetometers, which will contribute to achieving related quantum information processing based on defective diamonds.