Robust 1-μm-Resolution Magnetic Probe Enabled by Optical Trapping of Nanodiamonds on a Tapered Fiber

High-resolution magnetic field scanning is critical for investigating nanoscale spin systems and characterizing defects in microelectronic devices. We present a fabrication-free approach to create robust magnetic probes with 1-μm spatial resolution by synergizing the quantum magnetic sensitivity of nitrogen-vacancy (NV) centers in nanodiamonds with the enhanced photon efficiency of tapered fibers. Through gradient-force optical trapping, nanodiamonds are precisely positioned at the fiber tip, where van der Waals forces immobilize them without requiring micro-nanoprocessing. In addition to possessing high spatial resolution, the probe exhibits a magnetic sensitivity reaching $80\mu T/\sqrt{\mathrm{Hz}}$. By demonstrating a magnetic field scan of crossed microwires, this method can be extended to measure tiny magnetic structures or microcircuits, leveraging the integrated photonic enhancement of tapered fibers for robust high signal-to-noise sensing.