Ultrafast Reversal of a Fano Resonance in a Plasmon-Exciton System

TL;DR

This paper predicts that femtosecond pulsed lasers can ultrafastly reverse Fano resonances in a plasmon-exciton system, enabling dynamic control of optical properties through phase manipulation.

Contribution

It introduces a novel ultrafast control mechanism for Fano resonances in plasmon-exciton systems using pulsed laser illumination.

Findings

Femtosecond pulses can invert Fano resonance to superscattering.

Ultrafast phase changes cause the resonance reversal.

The effect is significant under thermal broadening conditions.

Abstract

When a two-level quantum dot and a plasmonic metal nanoantenna are resonantly coupled by the electromagnetic near field, the system can exhibit a Fano resonance, resulting in a transparency dip in the optical spectrum of the coupled system. We calculate the nonlinear response of such a system, for illumination both by continuous-wave and ultrafast pulsed lasers, using both a cavity quantum electrodynamics and a semiclassical coupled-oscillator model. For the experimentally relevant case of meV thermal broadening of the quantum-dot transition, we predict that femtosecond pulsed illumination can lead to a reversal of the Fano resonance, with the induced transparency changing into a superscattering spike in the spectrum. This ultrafast reversal is due to a transient change in the phase relationship between the dipoles of the plasmon and the quantum dot. It thus represents a new approach to dynamically control the collective optical properties and coherence of coupled nanoparticle systems.