Cavity polaritons originate from the strong coupling of excitons and light. When excited resonantly, they form macroscopically coherent states. Nonlinear interaction of polaritons involves optical multistability which manifests itself in sharp switches between alternative coherent states in response to varying excitation parameters. As a result, the intensity and polarization of the emitted light can be controlled on a very short (sub-nanosecond) timescale.

Owing to the Zeeman effect in a magnetic field, the polariton system has two branches of optical response that are characterized by opposite circular polarizations. Here, a new mechanism of polarization reversal is predicted, according to which the current state undergoes a transition to dynamical chaos and then the alternative spin state is established spontaneously. Such spin switches, which are mediated by a chaotic stage, proceed in both ways in the vicinity of the same critical point. As a result, the sign of the circular-polarization degree of the emitted light can be directly controlled by the intensity of optical pump.

The figure illustrates the switches between opposite-spin states under the conditions of a slow increase or decrease of the pump intensity as well as the chaotic dynamics of polarization at the intermediate stage; dashed lines are dynamically unstable solutions

Gavrilov S., Ipatov N., Kulakovskii V.
JETP Letters 118, issue 9 (2023)