Quadrupole-Quadrupole Interactions to Control Plasmon-Induced Transparency

From quantum optics, we are familiar with electromagnetically induced transparency (EIT), particularly in association with ``slow light''. The plasmonic analogue, PIT, now also receives attention due to its potential applications in sensing, communication, and more. However, the conventional dipole-quadrupole coupling yields only a modest quality factor $Ql100$. Here controlling the $Q$ factor of the Fano lineshape is not trivial. The authors demonstrate quadrupole-quadrupole interaction in engineered meta-atoms to control $Q$ and attain $Qg100$, with the potential to reach 1000, bringing high-$Q$ applications based on PIT one step closer.