An efficient method to create high-density nitrogen-vacancy centers in CVD diamond for sensing applications

Abstract

The negatively charged Nitrogen-Vacancy (NV$^−$) center in diamond is one of the most versatile and robust quantum sensors suitable for quantum technologies, including magnetic field and temperature sensors. For precision sensing applications, densely packed NV$^−$ centers within a small volume are preferable due to benefiting from 1/$√N$ sensitivity enhancement ($N$ is the number of sensing NV centers) and efficient excitation of NV centers. However, methods for quickly and efficiently forming high concentrations of NV$^−$ centers are in the development stage. We report an efficient method for creating high-density NV$^−$ centers production from a relatively low nitrogen concentration based on high-energy photons generated from Ar$^+$ plasma source. This study was done on type-IIa, single crystal, chemical vapor deposition (CVD)-grown diamond substrates with an as-grown nitrogen concentration of 1 × 10$^{17}$ cm$^{−3}$. We created high NV$^−$ density (~20,000 NVs over the diffraction limited sample volume) distributed homogeneously over 150–200 μm deep from the diamond surface. The plasma-created NV$^−$s in CVD diamond have a spin-lattice relaxation time (T$_1$) of 5 ms and a spin-spin coherence time (T$_2$) of 4 μs. We measure a DC magnetic field sensitivity of ∼104 nT Hz$^{-1/2}$, an AC magnetic field sensitivity of ∼0.12 pT Hz$^{-1/2}$ and demonstrate real-time magnetic field sensing at a rate over 10 mT s$^{−1}$ using the diffraction limited sample volume.