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Exciton-polaritons—coupled states of excitons and photons—exhibit interesting properties that may make them suitable as information carriers for optical computing technologies. With this goal in mind, Ballarini et al. demonstrate an all-optical polariton transistor that also operates as a logic gate.

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.

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.

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.

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.

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.

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 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.

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.

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.

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.

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.

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.

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.

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.

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.

Polaritons are an integral part of semiconductor optical devices and control of their inherent spin-like properties is necessary to explore the potential implications of this phenomenon. Here, the authors magnetically control the transport of polariton spin in a microcavity and explain the polarisation dynamics in terms of the polariton pseudospin.

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.