Polaritonic nonlocality in light–matter interaction

Subwavelength electromagnetic field localization has been central to photonic research in the last decade, allowing us enhance sensing capabilities as well increase coupling between photons and material excitations. The strong ultrastrong light–matter regime terahertz range using split-ring resonators coupled magnetoplasmons widely investigated, achieving successive world records for largest ever achieved. Ever shrinking have allowed approach of few-electron coupling, which single-dipole properties can be modified by vacuum field. Here, we demonstrate, theoretically experimentally, existence a limit possibility arbitrarily increasing confinement polaritonic systems. Strongly subwavelength fields excite continuum high-momenta propagative magnetoplasmons. This leads peculiar nonlocal effects, certain features disappear system enters discrete-to-continuum coupling. Extreme systems is demonstrated. tight result phenomena.