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

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.

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.

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.

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.

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.

Long-lived polariton condensates can propagate well beyond the area of their initial excitation while still maintaining spatial coherence. This enables direct and controllable manipulation of the condensate wavefunction.

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

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.

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.

Microcavity polaritons are a fluid of coupled photonic and electronic excitations that share many of the properties of Bose–Einstein condensates. Here, the authors show that the sudden creation of these bosonic fluids at high density results in the concentration of the particles, unlike an atomic gas that would expand.

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.

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.

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.

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

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.

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.