Ensemble Of Nitrogen-vacancy Centers In Diamond Research Articles

Enhanced sensitivity of the nitrogen-vacancy ensemble magnetometer via surface coating

Magnetometers based on nitrogen-vacancy center ensembles in diamond have received considerable attention in recent years. However, their sensitivities are limited by low fluorescence collection efficiencies. With the introduction of some schemes, collection efficiencies of NV ensembles have been improved, but further improvement is still needed. In this Letter, we propose and demonstrate a fluorescence enhancing technique of reflective coating. By applying this technique, collection efficiencies already improved by other schemes will be further enhanced. With the assistance of a 100-nm-thick gold reflective film on the diamond surface, the fluorescence collection efficiency of an NV ensemble continuous-wave magnetometer utilizing a compound parabolic concentrator was further increased by 92%, and a magnetic field sensitivity of 164 pT/Hz at 0.99 to 77.98 Hz was achieved.

Microwave Magnetic Field Coupling with Nitrogen-Vacancy Center Ensembles in Diamond with High Homogeneity

Electron spin resonance measurements with nitrogen-vacancy (NV) center ensembles in diamond are strongly dependent on a uniform microwave magnetic field. Three different types of microwave resonators are used and are well coupled with the spin ensembles at 2.87 GHz for zero-field splitting of the NV centers. The magnitude and the uniformity of both the horizontal and vertical magnetic fields are extracted and analyzed within a $$1\times 1\times 0.5$$ mm3 volume on a diamond sample surface, and the results indicate that the field homogeneity is up to 200 times better than that of the traditional copper wire microwave delivery model. The horizontal magnetic field magnitude homogeneity is better than 5 % over an area of 1 mm2 on the thin film diamond sample with NV ensembles. The average Rabi oscillation frequency is estimated to be 2.3 MHz per 1 W of microwave input power upon strong coherent coupling between the resonators and the spin ensembles. The effect of the nonuniform microwave magnetic field on the spin signal is also discussed. The approach used here will find widespread application in microwave coupling with spin ensembles in thin films.