excitonphoton

An exciton-photon, more commonly referred to as an exciton-polariton, is a quasiparticle that arises when a semiconductor exciton strongly couples to a confined photon mode in a microcavity or related photonic structure. In the strong-coupling regime, the exciton and photon mix to form new eigenstates, producing two polariton branches called the upper polariton and the lower polariton. The dispersion curves exhibit an avoided crossing, or Rabi splitting, whose size reflects the coupling strength between the matter and light components.

Exciton-polaritons are typically observed in semiconductor systems that place quantum wells or two-dimensional materials inside optical cavities formed by distributed Bragg reflectors or other resonators. Common materials include GaAs-based structures, GaN, ZnO, and various perovskites or transition metal dichalcogenides. Reported Rabi splittings range from a few to several tens of meV, depending on material quality and cavity design. The polariton’s properties are tunable by detuning the photon and exciton energies, altering the relative weights of the exciton and photon components.

Because the photonic part endows polaritons with an extremely small effective mass, they can achieve macroscopic quantum phenomena at comparatively high temperatures. The exciton component provides interactions, enabling nonlinear optical behavior. Applications and research directions include low-threshold polariton lasers, all-optical switching, quantum simulators for many-body physics, and studies of condensation, coherence, and superfluid-like flow in solid-state systems.