Ultrastrong coupling in the near field of complementary split-ring resonators

Abstract

Ultrastrong coupling of split ring resonators to the cyclotron transition in two-dimensional electron gases is studied in the terahertz regime, clarifying the importance of the resonator geometry. The use of the complementary type of resonator allows removal of the signal from the uncoupled areas. The experimental results are of spectacular quality and quantity. A record high light-matter coupling ratio (normalized vacuum Rabi frequency) of 0.87 is achieved.