Phys. Rev. Lett. 114, 193901 (2015)

Exciton–polaritons in microcavities are a candidate system for the realization of low-threshold coherent light sources and efficient switches. Inhomogeneity of the sample (introduced deliberately or otherwise) can result in more than one exciton–polariton centre. Kristian Rayanov and colleagues from New Zealand, the USA, Mexico and Korea, have theoretically proposed that interaction between just two exciton–polariton centres in the weak lasing regime can exhibit dynamics much more complex than well-known bifurcations. In particular, self-induced oscillations in the two-centre system may result in the emission of a frequency comb spectrum of coherent radiation. The frequency offset and line spacing of the combs are tunable. They suggest that filtering the high-frequency components of the emission might result in a new type of coherent THz emitter. The team also considered the effect of noise on the system, and showed that peaks can be broadened to the point that merging can occur if spacing is insufficient.