Citation: Kosionis, S.G.; Yannopapas, V.; Thanopulos, I.; Paspalakis, E. Resonance Fluorescence of a Quantum Dot near a Metallic Nanoparticle: Quantum Interference Effects. Mater. Proc. 2022, 9, 19. https://doi.org/10.3390/ materproc2022009019 Academic Editor: Guanying Chen Published: 22 April 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Proceeding Paper Resonance Fluorescence of a Quantum Dot near a Metallic Nanoparticle: Quantum Interference Effects † Spyridon G. Kosionis 1, * , Vassilios Yannopapas 2 , Ioannis Thanopulos 1 and Emmanuel Paspalakis 1 1 Materials Science Department, School of Natural Sciences, University of Patras, 26504 Patras, Greece; ithano@upatras.gr (I.T.); paspalak@upatras.gr (E.P.) 2 Department of Physics, National Technical University of Athens, 15780 Athens, Greece; vyannop@mail.ntua.gr * Correspondence: kosionis@upatras.gr; Tel.: +30-2610-996315 † Presented at the 3rd International Online-Conference on Nanomaterials, 25 April–10 May 2022; Available online: https://iocn2022.sciforum.net/. Abstract: In recent years, significant attention was given to the quantum or nonlinear optical prop- erties of semiconductor quantum dots coupled to plasmonic nanostructures. A phenomenon that was studied is the modification of the resonance fluorescence spectrum of the quantum dot by the presence of the plasmonic nanostructure. The most common plasmonic nanostructure studied is the metallic (mainly gold or silver) nanosphere and, in most studies, the quantum dot is modeled as a two- level quantum system. In this work, we model the quantum dot structure with a three-level V-type quantum system, which can naturally arise in quantum dots, and study the resonance fluorescence spectrum near a metallic nanosphere. We show that the present system leads to quantum interference effects due to the presence of the metallic nanoparticle and specifically due to the anisotropic Purcell effect that occurs in the photon emission of the quantum dot near the metallic nanosphere. We then study the resonance fluorescence spectrum for different distances between the quantum dot and the metallic nanosphere, and show that the resonance fluorescence spectrum changes significantly from a single-peak spectrum to a multipeak spectrum. The effects of quantum interference in the resonance fluorescence spectrum are also explored. Keywords: quantum dot; metallic nanoparticle; resonance fluorescence; quantum interference 1. Introduction In recent years, novel optical properties detected in hybrid systems which are com- posed of quantum emitters, such as molecules and quantum dots, and plasmonic (metallic or metal-dielectric) nanostructures attracted significant attention [1]. The coupling between excitons and surface plasmons can strongly modify a series of optical effects which, un- til recently, were explored in isolated quantum emitters. Among the various quantum optical effects studied in coupled quantum dot—plasmonic nanostructures, of particular interest is the modified incoherent spectrum of fluorescent photons emitted by a quantum dot near a metallic nanostructure and under laser excitation, i.e., the modification of the resonance fluorescence spectrum. This modification mainly occurs due to the alteration of the spontaneous decay rate of the quantum dot near the plasmonic nanostructure and the exciton–plasmon coupling. This effect was analyzed in quantum dots modeled by a two-level system [1,2], a Λ-type three-level system [3], as well as in more complex energy- level structures, such as the double-V-type [4] and the double-Λ-type four-level systems [5]. In these studies, the quantum dot was assumed to be coupled to either a single metallic nanosphere [1–3] or to more complicated plasmonic structures [4,5]. More specifically, in the double-V-type [4] and the double-Λ-type four-level systems [5], it was found that the anisotropic Purcell effect is responsible for creating quantum interference effects [6,7] which can also modify the resonance fluorescence spectrum. Mater. Proc. 2022, 9, 19. https://doi.org/10.3390/materproc2022009019 https://www.mdpi.com/journal/materproc