Atomic-Scale Visualization and Manipulation of Nitrogen-Vacancy Centers in Nanodiamonds*

Nitrogen vacancy (NV) centers in diamond have emerged as a leading candidate for qubit applications due to their millisecond spin coherence times and optical addressability. While previous work has primarily focused on NVs in bulk diamond, a new direction involves integration of NV charge centers in nanometer-scale diamond particles, termed nanodiamonds. NV centers embedded in nanodiamonds are highly photostable, and the nanoparticles themselves are highly mobile, providing a novel platform for quantum information and imaging applications. Despite intense research efforts, however, an atomic scale picture of the electronic states in nanodiamond NV centers has remained elusive. In our work, we first show the existence and distribution of NV centers in individual nanodiamonds using tip-enhanced Raman spectroscopy and photoluminescence. We then use scanning tunneling microscopy and spectroscopy to visualize the local electronic density-of-states (DOS) of NV centers in nanodiamonds on an atomic scale. We further probe changes in the defects' atomic-scale DOS under 532 nm laser illumination, thus providing valuable insights for future quantum information applications of NV centers in nanodiamonds.