Physics

Polariton

Photon

Superfluidity

Photonics

Condensed matter physics

Coherence (philosophical gambling strategy)

Bose–Einstein condensate

Quantum mechanics

Optoelectronics

Dissipative system

Nature Reviews Physics

The study of Bose–Einstein condensation effects in photonic systems has revealed a rich phenomenology related to spontaneous coherence generation in driven-dissipative spatially extended systems and is providing a new platform for the study of non-equilibrium phase transitions and critical behaviours. In this Review, we give an interdisciplinary overview of condensation phenomena in photonic systems. We cover a wide range of systems, from lasers to photon condensates in dye-filled cavities, to excitons in semiconductor heterostructures, to microcavity polaritons, as well as emerging systems, such as mode-locked lasers and classical light waves. Our aim is to highlight novel universal phenomena that stem from the driven-dissipative, non-equilibrium nature of these systems and affect the static, dynamic, superfluid and coherence properties of the condensate. Finally, we provide our perspectives on the future of fundamental science and technological applications in this field. The study of Bose–Einstein condensation in photonic systems has attracted strong interest in a variety of physical platforms, including conventional lasers and optical parametric oscillators, exciton and exciton–polariton gases, and photons in dye-filled cavities and propagating geometries. The focus of this Review is to highlight those universal phenomena that stem from the driven-dissipative, non-equilibrium nature of these systems and affect the static, dynamic, superfluid and coherence properties of the condensate.

Non-equilibrium Bose–Einstein condensation in photonic systems