excitonpolaritons

Exciton-polaritons are quasiparticles that arise from the strong coupling between excitons, bound electron-hole pairs in a semiconductor, and photons confined in an optical microcavity or a waveguide. When the exciton energy and a cavity photon mode are near resonance and the light-matter coupling strength exceeds the losses, the two systems hybridize to form two new eigenstates, known as the lower polariton and upper polariton branches. The energy-momentum dispersion exhibits an anticrossing and a characteristic Rabi splitting.

Due to their photonic component, exciton-polaritons have an extremely small effective mass compared with excitons, enabling macroscopic quantum effects at elevated temperatures relative to atomic systems. They inherit strong exciton nonlinearity, allowing interactions, scattering, and relaxation processes that drive nonlinear optical phenomena. In addition, finite lifetimes from photon leakage mean they typically exist in driven-dissipative, out-of-equilibrium conditions.

Exciton-polaritons have been observed in various material platforms, including semiconductor quantum wells embedded in planar microcavities (such as GaAs and GaN), perovskites, and organic semiconductors, as well as in waveguide geometries. These systems can support long-range coherence and, under appropriate pumping, polariton condensation or polariton lasing.

Applications and ongoing research focus on low-threshold light sources, all-optical switches and transistors, and quantum simulators of many-body physics. Fundamental studies explore superfluidity, vortices, and non-equilibrium phase transitions in driven-dissipative polariton fluids.