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We investigate the quantum-optical properties of the light emitted by a nanoparticle-on-mirror cavity filled with a single quantum emitter. Inspired by recent experiments, we model a dark-field set-up and explore the photon statistics of the scattered light under grazing laser illumination. Exploiting analytical solutions to Maxwell's equations, we quantize the nanophotonic cavity fields and describe the formation of plasmon exciton polaritons (or plexcitons) in the system. This way, we reveal that the rich plasmonic spectrum of the nanocavity offers unexplored mechanisms for nonclassical light generation that are more efficient than the resonant interaction between the emitter natural transition and the brightest optical mode. Specifically, we find three different sample configurations in which strongly antibunched light is produced. Finally, we illustrate the power of our approach by showing that the introduction of a second emitter in the platform can enhance photon correlations further.

We investigate plasmon-emitter interactions in a nanoparticle-on-a-mirror cavity. We consider two different sorts of emitters, those that sustain dipolar transitions, and those hosting only quadrupolar, dipole-inactive, excitons. By means of a fully analytical two-dimensional transformation optics approach, we calculate the light-matter coupling strengths for the full plasmonic spectrum supported by the nanocavity. We reveal the impact of finite-size effects in the exciton charge distribution and describe the population dynamics in a spontaneous emission configuration. Pushing our model beyond the quasi-static approximation, we extract the plasmonic dipole moments, which enables us to calculate the far-field scattering spectrum of the hybrid plasmon-emitter system. Our findings, tested against fully numerical simulations, reveal the similarities and differences between the strong coupling phenomenology for bright and dark excitons in nanocavities.

We investigate the impact that light-forbidden exciton transitions have in the near-field population dynamics and far-field scattering spectrum of hybrid plasmon-emitter systems. Specifically, we consider a V-type quantum emitter, sustaining one dipolar and one quadrupolar (dipole-inactive) excited states, placed at the nanometric gap of a particle-on-a-mirror metallic cavity. Our fully analytical description of plasmon-exciton coupling for both exciton transitions enables us to reveal the conditions in which the presence of the latter greatly alters the Purcell enhancement and Rabi splitting phenomenology in the system.

We investigate how the local density of states in a plasmonic cavity changes due to the presence of a distorting quantum emitter. To this end, we use first-order scattering theory involving electromagnetic Green’s function tensors for the bare cavity connecting the positions of the emitter that distorts the density of states and the one that probes it. The confined, quasistatic character of the plasmonic modes enables us to write the density of states as a Lorentzian sum. This way, we identify three different mechanisms behind the asymmetric spectral features emerging due to the emitter distortion: the modification of the plasmonic coupling to the probing emitter, the emergence of modal-like quadratic contributions and the absorption by the distorting emitter. We apply our theory to the study of two different systems (nanoparticle-on-mirror and asymmetric bow-tie-like geometries) to show the generality of our approach, whose validity is tested against numerical simulations. Finally, we provide an interpretation of our results in terms of a Hamiltonian model describing the distorted cavity.

Photobleaching is an effect terminating the photon output of fluorophores, limiting the duration of fluorescence-based experiments. Plasmonic nanoparticles (NPs) can increase the overall fluorophore photostability through an enhancement of the radiative rate. In this work, we use the DNA origami technique to arrange a single fluorophore in the 12-nm gap of a silver NP dimer and study the number of emitted photons at the single molecule level. Our findings yielded a 30× enhancement in the average number of photons emitted before photobleaching. Numerical simulations are employed to rationalize our results. They reveal the effect of silver oxidation on decreasing the radiative rate enhancement.

When arranged in a periodic geometry, arrays of metallic nanostructures are capable of supporting collective modes known as lattice resonances. These modes, which originate from the coherent multiple scattering between the elements of the array, give rise to very strong and spectrally narrow optical responses. Here, we show that, thanks to their collective nature, the lattice resonances of a periodic array of metallic nanoparticles can mediate an efficient long-range coupling between dipole emitters placed near the array. Specifically, using a coupled dipole approach, we calculate the Green tensor of the array connecting two points and analyze its spectral and spatial characteristics. This quantity represents the electromagnetic field produced by the array at a given position when excited by a unit dipole emitter located at another one. We find that, when a lattice resonance is excited, the Green tensor is significantly larger and decays more slowly with distance than the Green tensor of vacuum. Therefore, in addition to advancing the fundamental understanding of lattice resonances, our results show that periodic arrays of nanostructures are capable of enhancing the long-range coupling between collections of dipole emitters, which makes them a promising platform for applications such as nanoscale energy transfer and quantum information processing.