Characterization of low-nitrogen quantum diamond for pulsed magnetometry applications

Ensembles of nitrogen-vacancy (NV) centers in diamond are versatile quantum sensors with broad applications in the physical and life sciences. The concentration of neutral substitutional nitrogen ([Nₛ⁰]) strongly influences coherence times, sensitivity, and optimal sensing strategies. Diamonds with [Nₛ⁰] ~\,1-10\,ppm are a focus of recent material engineering efforts, with higher concentrations being favorable for continuous-wave optically detected magnetic resonance (CW-ODMR) and lower concentrations expected to benefit pulsed magnetometry techniques through extended NV electronic spin coherence times and improved sensing duty cycles. In this work, we synthesize and characterize low-[Nₛ⁰] (~\,0.8\,ppm), NV-enriched diamond material, engineered through low-strain chemical vapor deposition (CVD) growth on high-quality substrates, ¹²C isotopic purification, and controlled electron irradiation and annealing. Our results demonstrate good strain homogeneity in diamonds grown on CVD substrates and spin-bath-limited NV dephasing times. By measuring NV spin and charge properties across a wide range of optical NV excitation intensity, we provide direct comparisons of photon-shot-noise-limited magnetic sensitivity between the current low-[Nₛ⁰] and previously studied higher-[Nₛ⁰] (~\,14\,ppm) NV-diamond sensors. We show that low-[Nₛ⁰] diamond can outperform higher-[Nₛ⁰] diamond at moderate and low optical NV excitation intensity. Our results provide practical benchmarks and guidance for selecting NV-diamond sensors tailored to specific experimental constraints and sensing requirements.