Tunable optical activity in three-level nonchiral terahertz nanostructures under symmetrical incidence

We develop a theory of original quantum mechanism for finding strong optical activity quantum optical system in three-level non-chiral nanostructures, where symmetrical incidence (the propagation of the incident light is vertical to the plane of nanostructures) is considered. The theory is validated via both analytical and numerical analysis of specifically designed non-chiral coupled quantum dots models. In particular, by proper designing of the incidence, tunable terahertz wave polarized even in the opposite direction of the incidence is obtained. The effect could be explored for developing novel highly efficient terahertz polarization rotator and modulators, and may lead to the appearance of a new class of negative index terahertz nanostructures.