Diamond Nitrogen-Vacancy Center Ensembles for Wide-Field Magnetic Imaging: Optimizing Sensitivity through Diamond Growth*

Nitrogen-vacancy (NV) centers are promising quantum sensors for magnetic sensing. In one modality, which has important utility for condensed matter and biological systems, high-density NV ensembles can realize rapid, noninvasive, and highly-sensitive wide-field magnetic imaging with micron-scale spatial resolution. An outstanding challenge is to increase the NV ensemble sensitivity while maintaining spatial resolution. The fundamental sensitivity for an NV ensemble (η) scales inversely with the number of centers in the sensing volume (N) and inversely with NV coherence time (T₂^*): (η α 1/√(T₂^* N)). I will present our recently developed diamond growth and NV formation techniques that aim to increase the density of NV center ensembles while retaining their long coherence times, thus increasing the sensitivity of our magnetometer. Combining nitrogen δ-doped diamond and electron irradiation from a transmission electron microscope, the sensitivity of our ensemble NV magnetometers approaches sub nanoTesla/√Hz sensitivity in a 5x5x0.5 μm³ volume.