Nanowerk  March 20, 2023 The nonlinearity provided by the atom leads to a strong dependence of the light–matter interface on the number of photons interacting with the two-level system within its emission lifetime. This nonlinearity unveils strongly correlated quasiparticles known as photon bound states, giving rise to key physical processes such as stimulated emission and soliton propagation. Although signatures consistent with the existence of photon bound states have been measured in strongly interacting Rydberg gases their hallmark excitation-number-dependent dispersion and propagation velocity have not yet been observed. An international team of researchers (Switzerland, Australia, Germany) has reported the direct observation […]