Strong coupling of second harmonic generation scattering spectrum in a diexcitionic nanosystem

Diexcitonic strong coupling between quantum emitters and localized surface plasmon has attracted more attention recently because it can provide multiple qubit states for future quantum information technology at room temperature. In a strong coupling regime, nonlinear optical effects can offer new routes for developing quantum devices, but it is rarely reported. In this paper, we established the hybrid system consisting of J-aggregates-WS₂-cuboid Au@Ag nanorods, which can realize diexcitonic strong coupling and second harmonic generation (SHG). We find that multimode strong coupling has been achieved not only in the fundamental frequency scattering spectrum but also in the SHG scattering spectrum. SHG scattering spectrum shows three plexciton branches, similar to the splitting in the fundamental frequency scattering spectrum. Furthermore, the SHG scattering spectrum can be modulated by tuning the armchair direction of the crystal lattice, pump polarization direction, and plasmon resonance frequency, which makes our system very promising in the quantum device at room temperature. Moreover, we develop coupled nonlinear harmonic oscillator model theory to explain the nonlinear diexcitonic strong coupling mechanism. The calculated results by the finite element method accord well with our theory. The nonlinear optical properties of the diexcitonic strong coupling can provide potential applications such as quantum manipulation, entanglement, and integrated logic devices.