Second-Harmonic Generation from a Quantum Emitter Coupled to a Metallic Nanoantenna

We use time-dependent density functional theory and a semiclassical model to study second-harmonic generation in a system comprising a quantum emitter and a spherical metallic nanoparticle, where the transition frequency of the quantum emitter is set to be resonant with the second harmonic of the incident frequency. The quantum emitter is shown to enable strong second-harmonic generation, which is otherwise forbidden because of symmetry constraints. The time-dependent density functional theory calculations allow one to identify the main mechanism driving this nonlinear effect, where the quantum emitter plays the role of an optical resonator that experiences the nonlinear near fields generated by the metallic nanoantenna located nearby. The influence of the intrinsic properties of the quantum emitter and the nanoantenna, together with the relative position of both in the coupled system, allows for a high degree of control of the nonlinear light emission. The main effects and contributions to this nonlinear process can be correctly captured by a semiclassical description developed in this work.