Nonlinear nano-optical devices based on coupled quantum emitter arrays*

Subwavelength arrays of quantum emitters feature unique and largely designable nonlinear optical properties. In particular, absorption and emission properties of nanoscopic ring structures offer unique possibilities. As striking example we identify a sub-wavelength sized ring of exactly 9 identical dipoles with an extra identical emitter with a extra loss channel at the center as the most efficient antenna configuration to direct incoming photons to the center without reemission.

The enhancement is most pronounced a given resonance frequency but still stays visible for broadband light absorption. For very tiny structures below a tenth of a wavelength a full quantum description exhibits a larger enhancement than predicted from a classical dipole approximation.

The origin of the effect lies in the appearance of a collective dark state with dominant center occupation. By special design of the center absorber one can harness the same efficiency enhancement also at different wavelengths and for other geometric structures.

On the one hand this could be the basis of a new generation of highly efficient and selective nano antennas while on the other hand it could be an important piece towards understanding the surprising efficiency of natural light harvesting molecules. Adding gain in nano ring systems allows to design minimalistic classical as well as non-classical light sources.