Hybrid photonic-plasmonic cavities based on the nanoparticle-on-a-mirror configuration

[EN] Hybrid photonic-plasmonic cavities have emerged as a new platform to increase light-matter interaction capable to enhance the Purcell factor in a singular way not attainable with either photonic or plasmonic cavities separately. In the hybrid cavities proposed so far, the plasmonic element is usually a metallic bow-tie antenna, so the plasmonic gap-defined by lithography-is limited to minimum values of several nanometers. Nanoparticle-on-a-mirror (NPoM) cavities are far superior to achieve the smallest possible mode volumes, as plasmonic gaps smaller than 1 nm can be created. Here, we design a hybrid cavity that combines an NPoM plasmonic cavity and a dielectric-nanobeam photonic crystal cavity operating at transverse-magnetic polarization. The metallic nanoparticle can be placed very close (<1 nm) to the upper surface of the dielectric cavity, which acts as a low-reflectivity mirror. We demonstrate through numerical calculations of the local density of states that this hybrid plasmonic-photonic cavity exhibits quality factors Q above 10(3) and normalized mode volumes V down to 10(-3), thus resulting in high Purcell factors (F-P approximate to 10(5)), while being experimentally feasible with current technology. Our results suggest that hybrid cavities with sub-nanometer gaps should open new avenues for boosting light -matter interaction in nanophotonic systems.Horizon 2020 Framework Programme (829067 THOR); Generalitat Valenciana (PPC/2018/002, PROMETEO/2019/123); Ministerio de Ciencia, Innovacion y Universidades (PGC2018-094490-B, PRX18/00126); Alexander von Humboldt-Stiftung.Barreda, ÁI.; Zapata-Herrera, M.; Palstra, IM.; Mercadé-Morales, L.; Aizpurua, J.; Koenderink, AF.; Martínez Abietar, AJ. (2021). Hybrid photonic-plasmonic cavities based on the nanoparticle-on-a-mirror configuration. Photonics Research. 9(12):2398-2419. https://doi.org/10.1364/PRJ.433761S2398241991

Hybrid cavity-antenna systems for quantum optics outside the cryostat?

Hybrid cavity-antenna systems have been proposed to combine the sub-wavelength light confinement of plasmonic antennas with microcavity quality factors Q. Here, we examine what confinement and Q can be reached in these hybrid systems, and we address their merits for various applications in classical and quantum optics. Specifically, we investigate their applicability for quantum-optical applications at noncryogenic temperatures. To this end we first derive design rules for hybrid resonances from a simple analytical model. These rules are benchmarked against full-wave simulations of hybrids composed of state-of-the-art nanobeam cavities and plasmonic-dimer gap antennas. We find that hybrids can outperform the plasmonic and cavity constituents in terms of Purcell factor, and additionally offer freedom to reach any Q at a similar Purcell factor. We discuss how these metrics are highly advantageous for a high Purcell factor, yet weak-coupling applications, such as bright sources of indistinguishable single photons. The challenges for room-temperature strong coupling, however, are far more daunting: the extremely high dephasing of emitters implies that little benefit can be achieved from trading confinement against a higher Q, as done in hybrids. An attractive alternative could be strong coupling at liquid nitrogen temperature, where emitter dephasing is lower and this trade-off can alleviate the stringent fabrication demands required for antenna strong coupling. For few-emitter strong-coupling, high-speed and low-power coherent or incoherent light sources, particle sensing and vibrational spectroscopy, hybrids provide the unique benefit of very high local optical density of states, tight plasmonic confinement, yet microcavity Q