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Coupled semiconductor microcavities constitute a model system where the hopping, interaction, and decay of exciton polaritons can be engineered. Here, Rodriguez et al. show how the phase acquired by polaritons hopping between cavities can be controlled through polariton-polariton interactions.

Quantum fluids such as cavity-polaritons show nonlinear optical properties of interest in applications such as quantum optics. Here, Sturm and colleagues demonstrate an optical control of the phase of a polariton flow, and make use of this to realize a compact exciton–polariton interferometer.

Based on optically breaking time-reversal symmetry by spin polarizing a gain medium with a circularly polarized optical pump, an integrated scheme for controlling the chirality of orbital angular momentum lasing is demonstrated.

Bright and tunable single-photon sources are essential for future quantum technologies. Here, the authors deterministically couple a quantum dot to a pillar structure that enables application of electric fields to provide a tunable single-photon source with a demonstrated extraction efficiency of 53%.

Quantum information processing requires a system in which a single photon controls a single atom and vice versa. Here, the authors demonstrate such reciprocal operation and achieve coherent manipulation of a quantum dot by a few photons sent on an optical cavity.

For quantum technologies to become widespread and scalable, bright sources of indistinguishable single photons are essential. Through deterministic positioning of quantum dots in pillar cavities, Gazzano et al.present a solid-state single-photon source with brightness as large as 0.65 photons per pulse.

Squeezed and entangled light are necessary for quantum information applications. Here, working towards the practical application of such schemes, Boulier and colleagues demonstrate the generation of squeezed light from exciton-polaritons in a semiconductor micropillar.

Topologically protected lasing is reported in a lattice of polariton micropillars.

A single photon with near-unity indistinguishability is generated from quantum dots in electrically controlled cavity structures. The cavity allows for efficient photon collection while application of an electrical bias cancels charge noise effects.

Quantum emitters have recently been identified as efficient sources of graph states, which are entangled states crucial for photonic quantum computation. Here the authors demonstrate deterministic and reconfigurable generation of caterpillar graph states using a semiconductor quantum dot in a cavity.

Light-matter interfaces implementing arbitrary conditional operations on incoming photons would have several applications in quantum computation and communications. Here, the authors demonstrate conditional polarization rotation induced by a single quantum dot spin embedded in an electrically contacted micropillar, spanning up to a pi flip.

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.

A three-partite cluster state made of one semiconductor spin and two indistinguishable photons is generated from an InGaAs quantum dot embedded in a pillar microcavity. The three-partite entanglement rate is 0.53 MHz at the output of the device.

The Josephson effects that arise when two quantum states are coupled through a barrier are difficult to observe in optical systems because photon–photon interactions are so weak. Researchers have now demonstrated an optical realization of two such phenomena—macroscopic self-trapping and Josephson oscillations—using polariton condensates in overlapping microcavities.

Generating photonic cluster states using a single non-heralded source and a single entangling gate would optimise scalability and reduce resource overhead. Here, the authors generate up to 4-photon cluster states using a quantum dot coupled to a fibre loop, with a fourfold generation rate of 10 Hz.

Following excitation with a resonant laser, on-demand generation of non-classical light states in photon-number superpositions of zero-, one- and two-photon Fock states is demonstrated from a GaAs-based cavity containing InAs quantum dots.

Using ∼1-mm-long photonic crystal waveguides, scientists experimentally demonstrate the compression of 3 ps pulses to a minimum duration of 580 fs at a low pulse energy of ∼20 pJ. The approach may pave the way for soliton applications in integrated photonic chips.

Cavity polaritons, arising from strong coupling between light and matter in semiconductor structures, exhibit interesting and exotic phenomena. Tanese et al. study a polariton condensate in a periodic one-dimensional microcavity and find gap soliton states, which may be useful for polaritonic circuits.

The localization properties of waves in the quasiperiodic chains described by the Aubry–André model and Fibonacci model are investigated. Passing from one model to the other, the system develops a cascade of delocalization transitions.