A miniaturized magnetic field sensor based on nitrogen-vacancy centers (2402.19372v3)

Abstract: The nitrogen-vacancy (NV) center in diamond is a prime candidate for quantum sensing technologies. Here, we present a fully integrated and mechanically robust fiber-based endoscopic sensor with a tip diameter of $1.25 \mathrm{mm}$. On its tip, a direct laser writing process is used to fixate a diamond containing NV centers above the fiber's core inside a polymer structure. Additionally, a metallic direct laser-written antenna structure next to the fiber facet allows efficient microwave manipulation of NV center spins. The sensor achieves a shot-noise limited magnetic field sensitivity of $5.9 \mathrm{nT}/ \sqrt{\mathrm{Hz}}$ using a $15 \mathrm{\mu m}$-sized microdiamond at a microwave power of $50 \mathrm{mW}$ and optical power of $2.15 \mathrm{mW}$. Furthermore, we introduce a dual-fiber concept that enables, in combination with a direct laser-written structure, independent guiding of excitation and fluorescence light and thus reduces background autofluorescence. While the demonstrated sensitivity is achieved using a single-fiber configuration, the dual-fiber approach provides a path towards integrating smaller diamonds, where autofluorescence would otherwise limit performance. We demonstrate the capability of vector magnetic field measurements in a magnetic field as used in state-of-the-art ultracold quantum gas experiments, opening a potential field in which high resolution and high sensitivity are necessary.