Tuning photonic nanocavities by atomic force microscope nano-oxidation

The authors demonstrate a technique to achieve high-precision tuning of photonic crystal nanocavities by atomic force microscope nano-oxidation of the cavity surface. Relative tuning between two nanocavity modes is achieved though careful choice of the oxide pattern, allowing them to restore the spectral degeneracy conditions necessary to create polarization-entangled quantum states. Tuning steps less than the linewidth $\left(1\mathrm{\AA }\right)$ of the high quality factor modes are obtained, allowing for virtually continuous tuning ability.