Optical activity and circular dichroism of a hybrid system composed of a chiral quantum dot and a dielectric nanoparticle

Abstract

We study a hybrid system composed of a chiral quantum dot and a dielectric nanoparticle subjected to an electromagnetic wave. We aim to show that the hybrid system features synergistic properties caused by interactions between its components. We solve the Bloch equation for the density matrix of the chiral quantum dot modeled as a two-level system with transition electric and magnetic dipole moments. We show that the system acts as a bianisotropic meta-atom: The electric polarization (magnetization) can be induced by the incident magnetic (electric) field. The electromagnetic and magnetoelectric polarizability dyadics of the hybrid system are influenced by the nanoparticle size and separation and the intensity and polarization of the incident wave. Due to the self-interaction of the quantum dot in the presence of the nanoparticle, the system exhibits optical activity and circular dichroism spectra of different character in Fano, double peaks, weak transition, and strong transition regions of the parameter space. Notably, in the strong transition region, the optical activity and circular dichroism spectra become discontinuous and dependent on the initial state of the system. The magnetic dipole moment induced in the dielectric nanoparticle plays a key role: Indeed, unlike the isolated chiral quantum dot, the hybrid system exhibits strong circular dichroism in a broad frequency range. The chiral quantum dot-dielectric nanoparticle meta-atom offers unique opportunities for creating low-loss all-dielectric meta-surfaces operating in the visible spectral range.