  Fiber-coupled sensors are well suited for sensing and microscopy in
hard-to-reach environments such as biological or cryogenic systems. We
demonstrate fiber-based magnetic imaging based on nitrogen-vacancy (NV) sensor
spins at the tip of a fiber-coupled diamond nanobeam. We incorporated angled
ion implantation into the nanobeam fabrication process to realize a small
ensemble of NV spins at the nanobeam tip. By gluing the nanobeam to a tapered
fiber, we created a robust and transportable probe with optimized optical
coupling efficiency. We demonstrate the imaging capability of the fiber-coupled
nanobeam by measuring the magnetic field generated by a current-carrying wire.
With its robust coupling and efficient readout at the fiber-coupled interface,
our probe could allow new studies of (quantum) materials and biological
samples.
