Thermal Noise Spectrum for Near-Surface Nitrogen Vacancy Diamonds with Liquid Top Layer

Nitrogen vacancy center diamonds have become a popular topic recently with their applications in magnetic field sensors and quantum computing. Experiments have found that noise becomes a serious problem when an NV center is placed near the surface. This noise arises from fluctuations in both the electric and magnetic fields. We investigated the electric field noise caused by thermal fluctuation since it will be the main cause of noise at room temperature. Our model consisted of the NV-center with liquid on the surface. We examined three-different surface liquids; water/air, D-glycerol, and propylene carbonate to compare with recent experiments [PRL 115, 087602 (2015)]. Using the fluctuation dissipation theorem, we obtained the noise spectrum. At low frequencies, less noise is generated for glycerol and propylene carbonate than water/air. However, while water and propylene carbonate begin to follow a power law 1/ω^1.5 around 0.1 MHz reducing noise further, glycerol’s power law is much weaker and soon reaches relatively constant noise. Throughout the noise spectrum, propylene carbonate has the best reduction in noise until frequencies reach 10 MHz. At this point, water drops lower than propylene carbonate as the two noise spectra begin to flatten.