  Individual, luminescent point defects in solids so called color centers are
atomic-sized quantum systems enabling sensing and imaging with nanoscale
spatial resolution. In this overview, we introduce nanoscale sensing based on
individual nitrogen vacancy (NV) centers in diamond. We discuss two central
challenges of the field: First, the creation of highly-coherent, shallow NV
centers less than 10 nm below the surface of single-crystal diamond. Second,
the fabrication of tip-like photonic nanostructures that enable efficient
fluorescence collection and can be used for scanning probe imaging based on
color centers with nanoscale resolution.
