Non-equilibrium quantum plasmonics in nanoparticle-on-mirror nanocavities

We develop a novel approach to ultrafast optical modulation of quantum-mechanical phenomena at the interface of plasmonic metals. Focusing on efficient and versatile nanoparticle-on-mirror plasmonic nanocavities, we discuss indirect control of plasmonic properties through laser-induced ballistic hot electron injection. Overcoming the limitations precluding the observations of laser-driven mesoscopic phenomena in the time domain with state-of-the-art amplified sources, our proposed experimental approach can be readily realized without irreversible optical damage and holds immense potential for the future development of ultrafast electrodynamics in nanogaps, applications in photochemistry and nanoscale control of quantum emitters. Agreeing with the results of numerical simulations, an intuitive microscopic model for the proposed time-dependent mesoscopic electrodynamics facilitates the analysis of the temperature-induced modulation of quantum plasmonic properties in a broad parameter space. Our work expands the realm of quantum nanophotonics onto non-equilibrium electronic systems and facilitates the development of ultrafast methods in active plasmonics.