Influence of a planar metal nanoparticle assembly on the optical response of a quantum emitter

We develop an analytical framework to study the influence of a weakly intercoupled in-plane spherical metal nanoparticle (MNP) assembly on a coherently illuminated quantum emitter (QE). We reduce the analytical expressions derived for the aforementioned generic planar setup into simple and concise expressions representing a QE mediated by a symmetric MNP constellation, by exploiting the symmetry. We use the recently introduced generalized nonlocal optical response (GNOR) theory that has successfully explained plasmonic experiments to model the MNPs in our system. Due to the use of GNOR theory, and our analytical approach, the procedure we suggest is extremely computationally efficient. Using the derived model, we analyze the absorption rate, resultant Rabi frequency, effective excitonic energy shift, and dephasing rate shift spectra of an exciton bearing QE at the center of a symmetric MNP setup. We observe that the QE experiences plasmon-induced absorption rate spectral linewidth variations that increase in magnitude with decreasing MNP-QE center separation and increasing number of MNPs. Our results also suggest that parameter regions where the QE exhibits trends of decreasing linewidth against decreasing MNP-QE center separation are likely to be associated with plasmon-induced excitonic energy redshifts. Similarly, regions where the QE absorption rate linewidth tends to increase against decreasing MNP-QE center separation are likely to be accompanied by plasmon-induced excitonic energy blueshifts. In both these cases, the magnitude of the observed redshift and blueshift was seen to increase with the number of MNPs in the constellation, due to enhancement of the plasmonic influence. We show that even when the magnitude of the QE absorption rate spectrum is much smaller compared to the isolated (collective) MNP spectra, it is sufficient to dramatically modify the spectrum of the MNP-QE nanohybrid, causing sharp Fano-type interference patterns.