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This work creates a magnon-photon interface from a 2D magnetic semiconductor metasurface. It demonstrates both the static and ultrafast control of exciton polaritons with spins and coherent magnons, paving the way for spin-based photonic devices.

Three-dimensional helical chiral metamaterials are required for nanophotonics but lack of full rotational symmetry has limited their use. Here, Esposito et al. combine chirality and isotropy, fabricating intertwined helical nanowires with 37% broadband circular dichroism with a high signal to noise ratio.

The Berezinskii–Kosterlitz–Thouless transition is observed in a 2D gas of exciton-polaritons, through measurements of the first-order coherence both in space and time.

A room-temperature double-layer WS₂ microcavity is used to explore spin anisotropy and tune it with interlayer spacing.

The authors report on the implementation of a photonic crystal waveguide with hyperbolic geometry supporting bound-in-the continuum exciton-polariton condensates. This unveils the coexistence of evanescent and ballistic polariton coupling behaviour with all-optical control.

The optical nature of exciton-polaritons enables new types of devices that leverage coherent quantum effects. Here the authors demonstrate a ring-shaped Josephson junction on a solid-state exciton-polariton platform, addressing challenges in generating polariton currents and providing optical access to the quantum phase. This advancement brings new possibilities for integrating the Josephson effect into photonic circuitry.

A method to fabricate arbitrarily shaped perovskite crystals is measured, apt for the realization of integrated photonic circuitry, demonstrating room-temperature waveguided exciton–polariton condensation and bright polariton edge lasing.

Similar to atoms in cold gases, exciton–polaritons in semiconductor microcavities can undergo Bose–Einstein condensation, but under non-equilibrium conditions. Now, quantized vortices and persistent currents — hallmarks of superfluid behaviour — have been observed in such condensates.

Bound-states-in-the-continuum (BICs) display unique features like symmetry protection from dissipation, long lifetimes and topological charges. Here the authors demonstrate anisotropic Bogoliubov excitation spectrum of polariton condensate from a BIC using a patterned semiconductor GaAs/AlGaAs waveguide.

Combining a tungsten disulfide monolayer and a topologically protected bound state in the continuum formed by a one-dimensional photonic crystal, strong light–matter interaction enhancement and large exciton–polariton nonlinearities at room temperature are demonstrated.

A hybrid state of photons and electronic excitations in semiconductor quantum wells shows nonlinear behaviour at the level of single or few quanta, thus opening the door to the realization of photonic nonlinear quantum devices employing semiconductor technologies.

Hybrid light–matter states at the surface of a 2D material can interact strongly and propagate over macroscopic distances.

Superfluidity is a phenomenon usually restricted to cryogenic temperatures, but organic microcavities provide the conditions for a superfluid flow of polaritons at room temperature.

Experimental evidence is presented for a new implementation of supersolidity in a driven-dissipative, non-equilibrium context realized in a photonic-crystal waveguide, demonstrating the breaking of translational symmetry with exceptionally low losses.

Here, the authors design a microcavity-confined 2D heterojunction to realize the strong coupling among donor exciton, acceptor exciton, and cavity photon mode, leading to an unconventional energy transfer via polariton relaxation with an enhancement factor of ~440.

The turbulent dynamics of a 2D quantum fluid of exciton–polaritons is measured in a planar AlGaAs microcavity after a pulsed optical excitation. Clear evidence of both the onset of vortex clustering and inverse energy cascade is provided.

Using a patterned waveguide, a Bose–Einstein condensate of polaritons is realized in a bound state in the continuum, with a low condensation threshold density that occurs at a dispersion saddle point.

Exciton-polaritons result from the strong coupling of excitons and photons, exhibiting strong nonlinearity. Here, Zhao et al demonstrate room-temperature optical polariton spin-switching in a tungsten disulfide superlattice.

Direct measurement of the Berry curvature and the quantum metric of photonic modes in a high-finesse planar microcavity is achieved, enabling quantitative prediction of the independently measured anomalous Hall drift.

Bound states in the continuum are topological states with useful symmetry protection properties. An experiment now shows how to use them to form macroscopically coherent complexes of polariton condensates.

The authors embed a multiple quantum-well WS₂ heterostructure in a planar microcavity and show the systematic control of the normal mode coupling-strength. They find a strong enhancement of the characteristic time scale, which they attribute to long-lived dark excitations emerging in the structure.

Engineering the energy dispersion of polaritons in microcavities can yield intriguing effects such as the anomalous quantum Hall and Rashba effects. Now, different Berry curvature distributions of polariton bands are obtained in a strongly coupled organic–inorganic two-dimensional perovskite single-crystal microcavity and can be modified via temperature and magnetic field variation.

Nonlinear optical parametric polaritons are observed in a WS₂ monolayer microcavity, opening the way for all-optical valley polariton nonlinear devices.

Polariton condensates undergo continuous driving and dissipation, posing challenges for investigating their collective behaviour. Ballarini et al. adapt an oceanographic technique to measure the asymmetric occupation of the Goldstone mode and identify similarities with equilibrium condensates.

All-optical control of the topological excitations of a superfluid of light is demonstrated in a high-quality-factor semiconductor microcavity. Recovery of superfluid behaviour at high polariton densities and bosonic Josephson vortices are observed.

Vortex–antivortex pairs in a polariton condensate are experimentally trapped and manipulated by a light beam in a semiconductor microcavity. Quantum hydrodynamical effects are observed and corroborated by time-dependent simulations.

Superfluid flow around a vortex is quantized so that vortices become discrete, particle-like defects, with interactions mediated by the surrounding fluid. Here, the authors use a polariton system to experimentally investigate the behavior and scattering of vortices in a two-component superfluid.

An outlook on the potential of lead-halide perovskites as a playground for exciton-polariton studies and for the development of polaritonic devices operating at room temperature is provided.

This review discusses exciton–polaritons in microcavities and their emerging technological applications, with emphasis on the materials challenges for operation at room temperature.

Phase vortices and skyrmions manifest as rotational entities in condensates, superfluids, and optics, typically revealed by the analysis of the Berry curvature. Via two-component microcavity polaritons, the authors imprint a dynamical pseudospin texture to the emitted light, generating a continuous vortex with two ultrafast spiraling cores.

Recently, observation of low-density polaritons in the quantum regime has prompted interest beyond their collective behavior. Here, an integrated quantum logic device that relies on two-body polaritonic interaction is proposed theoretically.

The review focuses on recent advances in TMD-based strong light-matter coupling, including the various optical structures strongly coupled to TMDs, several intriguing properties, and relevant device applications of TMD polaritons