Ultrastrong light-matter coupling at 300 GHz with few (<80) electrons

Abstract

We demonstrate ultrastrong light-matter coupling between less than 80 electrons located in the last occupied Landau level of an high mobility 2 dimensional electron gas and a LC resonator with an extremely small effective mode volume V eff /λ3 = 4 × 10−10. The unperturbed frequency is 300 GHz and the measured normalized coupling ratio is Ω/ω = 0.35.