Cooperative effects in complex, coupled quantum systems, cannot be understood by sole consideration of the individual constituents, as they arise from the interplay among them. Light-matter platforms provide an optimal playground for the observation and exploitation of quantum cooperative effects [1]. I will first refer to structured subwavelength arrays of quantum emitters, for example made by atoms trapped in optical lattices, exhibiting an optimized optical response stemming from the hopping of surface excitations via dipole-dipole interactions and by the modified radiative properties. The emergence of collective excitonic subradiant states, i.e states radiating at much smaller rates than isolated atoms, allows for the tuning of the optical response frequency window. In the opposite regime, where the radiative properties are strongly enhanced, a phenomenon known as superradiance, I will provide a simple theoretical description of the operation of a superradiant laser versus a standard laser.

[1] M. Reitz, C. Sommer, and C. Genes, Cooperative Quantum Phenomena in Light-Matter Platforms, PRX Quantum 3, 010201 (2022).