Dicke-Cooperativity-Assisted Ultrastrong Coupling Enhancement in Terahertz Metasurfaces.

A system of two-level atoms cooperatively interacting with a photonic field can be described as a single giant atom coupled to the field with interaction strength . This enhancement, known as Dicke cooperativity in quantum optics, has recently become an indispensable element in quantum information technology. Here, we extend the coupling beyond the standard light-matter interaction paradigm, enhancing Dicke cooperativity in a terahertz metasurface with meta-atoms.