Second-order nonlinearity in ladder-plus-Y configuration in double quantum dot structure

Second-order nonlinear susceptibility (SONS) in a ladder-plus-Y double quantum dot structure was modeled and then studied numerically under the application of an electric field. The density matrix theory was used to formulate the system while the orthogonalized plane waves for wetting layer-quantum dot (WL-QD) were considered to state the momentum matrix elements for this system. It is found that the momenta follow the smallest energy difference between states with an obvious overlap of the mediated states. Since WL-QD momenta are small, neglecting WL gives high SONS. Millimeter waves are predicted, and a huge SONS can be obtained by the application of more optical fields, which is important in medical and biological applications. The possibility of changing light speed between subluminal and superluminal was predicted here. This opens the way for many applications like multichannel waveguide-multichannel quantum information processing, real quality imaging, and temporal clock.