Revealing the quantum property of suppressed middle plexciton state in three-mode coupling system

Abstract

The three-mode coupling among excitons–surface plasmon(SP)–excitons has attracted extensive attention owing to its richer modulation capability compared to traditional two-mode coupling. However, the coupling mechanism of middle hybrid state in three-mode systems has not been clear. Here, we develop a full quantum theory based on the Jaynes–Cummings model to investigate the properties of middle plexciton branch (MPB) in excitons–SP–excitons system. The calculated scattering spectrum includes three plexciton branches, which shows that the MPB has the narrowest linewidth and lowest peak amplitude compared to the other two branches. The derived Hopfield coefficients demonstrate that the narrowest linewidth of MPB is due to its low SP fraction compared to that of excitons, which is different from the fractions of SP and excitons for the other two branches. The calculated results indicate that MPB peak amplitude is lowest because the detuning between two excitons is smaller than the coupling coefficient g, and MPB has the lowest population compared with those of the other two branches. Additionally, to verify our theory, we design an Au nanorod coated with two layers of J-aggregate nanoshells by the finite-difference time-domain (FDTD) simulation which results accord well with our theory. Our work has wide applications in quantum optical devices, quantum information, and quantum computing.