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The strong coupling of light and matter is responsible for phenomena such as Bose–Einstein condensation. In a study of strong-coupling effects in semiconductor microcavities, the interaction between a two-level electronic system and a light field has now been observed.

Strong coupling between a gated semiconductor quantum dot and an optical microcavity is observed in an ultralow-loss frequency-tunable microcavity device.

The Jaynes–Cummings model describes the interaction between a two-level system and a small number of photons. It is now shown that the model breaks down in the regime of ultrastrong coupling between light and matter. The spectroscopic response of a superconducting artificial atom in a waveguide resonator indicates higher-order processes.

The exploration of the Jaynes–Cummings Hamiltonian in a circuit-QED system—where an ‘artificial atom’ made of a superconducting circuit is strongly coupled to a microwave field—provides direct evidence for nonlinearities due to quantum mechanics on the level of single atoms and photons.

Hole spin qubits in germanium have seen significant advancements, though improving control and noise resilience remains a key challenge. Here, the authors realize a dressed singlet-triplet qubit in germanium, achieving frequency-modulated high-fidelity control and a tenfold increase in coherence time.

Researchers observe a continuous change in photon correlations from strong antibunching to bunching by tuning either the probe laser or the cavity mode frequency. These results, which demonstrate unprecedented strong single-photon nonlinearities in quantum dot cavity system, are explained by the photon blockade and tunnelling in the anharmonic Jaynes–Cummings model.

Microwave-mediated coupling of electron spins separated by more than 4 mm is demonstrated, suggesting the possibility of using photons at microwave frequencies to create long-range two-qubit gates between distant spins.

Quantum acoustics investigates the interaction between mechanical oscillators and superconducting qubits. Here, the authors demonstrate the generation of large-amplitude phonon states using quantum acoustics’ toolbox.

Researchers report the first demonstration of an ultrafast all-optical switch in the single-photon regime. The device, which consists of an InAs/GaAs quantum dot in a photonic crystal defect cavity, exhibits a coherent coupling constant of 141 meV and a quality factor of 25,000. The overall switching time is around 50 ps.

By coupling a spin-qubit to a superconducting resonator, remote spin-entanglement becomes feasible. Here, Ungerer et al achieve strong coupling between a superconducting resonator and a singlet-triplet spin qubit, in an InAs nanowire.

Microcavity exciton-polaritons in atomically thin semiconductors are a promising platform for valley manipulation. Here, the authors show valley-selective control of polariton energies in monolayer WS2 using the optical Stark effect, thereby extending coherent valley manipulation to a hybrid light-matter regime

Using an artificial three-level lambda system realized in a superconducting transmon qubit in a microwave cavity one can observe coherent population trapping, electromagnetically induced transparency and superluminal pulse propagation.

Manipulation of the photochemistry of molecules is traditionally achieved through synthetic chemical modifications. Here the authors use computational photochemistry to show how to control azobenzene photoisomerization through hybrid light–molecule states (polaritons).

A cavity quantum electrodynamics system comprising a quantum emitter and an optical cavity is theoretically investigated. The outcoupling process for the N-photon state of the cavity is simulated. The numerical calculations predict the possibility of operating this system as a source of N-photon bundles with a tunable integer N.

Controlling coupling between distant quantum objects is important for implementation of quantum technologies. Providing an important step towards using semiconductor structures for hosting optically controlled qubits, this work shows coherent coupling between three quantum dot excitons via a cavity.

Researchers propose that a cold atom in a one-dimensional photonic crystal waveguide can form a cavity. This system should allow interaction with other atoms within the effective cavity length.

Micrometre-scale superconducting circuits are at present explored as the building blocks for scalable quantum information processors. In a system where two such qubits are coupled to a resonant cavity, tripartite interactions and controlled coherent dynamics have now been demonstrated. This platform should allow for a fuller exploration of multipartite quantum states and their deterministic preparation.

Achieving ultrastrong coupling requires demanding experimental conditions such as cryogenic temperatures, strong magnetic fields, and high vacuum. Here, the authors use plasmon-microcavity polaritons to achieve ultrastrong coupling at ambient conditions and without the use of magnetic fields.

Conservation laws are a key ingredient in the non-equilibrium dynamics of quantum many-body systems. Here, the authors develop generalised quantum fluctuation relations in order to identify the presence of conserved quantities relevant for a generalised Gibbs ensemble.

A transmon qubit insensitive to magnetic fields is a crucial element in topological quantum computing. Here, Kroll et al. create graphene transmons by integrating monolayer graphene Josephson junctions into microwave frequency superconducting circuits, allowing them to operate in a parallel magnetic field of 1 T.

Hybrid quantum systems, such as superconducting qubits interacting with microwave photons in resonators, offer a rich platform for exploring fundamental physics. Wang et al. observe parity symmetry breaking in a probe qubit dispersively coupled to a resonator in the deep-strong coupling regime.

In this work, Manenti et al. present measurements of a device in which a tuneable transmon qubit is piezoelectrically coupled to a surface acoustic wave cavity, realising circuit quantum acoustodynamic architecture. This may be used to develop new quantum acoustic devices.

Pump-probe method is commonly used for studying ultrafast molecular dynamics. Here, the authors discuss alternative approach of using time-dependent ultrafast light emission from excited molecules coupled to a plasmonic nanocavity instead of using probe pulse.

Qubit-based simulations of gauge theories are challenging as gauge fields require high-dimensional encoding. Now a quantum electrodynamics model has been demonstrated using trapped-ion qudits, which encode information in multiple states of ions.

Single-photon optical nonlinearity is possible using an optical cavity to create strong coupling between a cavity mode and a two-level quantum system. Here, the authors demonstrate it is also possible in the weak-coupling regime by using quantum interference in a polarization-degenerate cavity.

Readout of a superconducting qubit embedded in a circuit quantum electrodynamics architecture is demonstrated at optical frequencies through a low-noise electro-optomechanical transducer.

Description of non-equilibrium phase transitions is problematic, due to the absence of suitable free energy landscapes. Here, the authors experimentally show delayed photon condensation and timing jitter in a dye-filled microcavity, modelled by a non-equilibrium extension of the free-energy landscape.

The second law of thermodynamics constrains how much of a conserved quantity, such as energy, can be extracted from a system in the form of work. Here, the authors generalize this law to quantum systems whose conserved quantities need not commute, showing that it is their combination to be constrained.

Networks of atom–cavity systems necessarily require that single atoms sit near dielectric interfaces. Real-time monitoring of caesium atoms just 100 nm from the surface of a micro-toroid resonator now demonstrates that the Casimir effect plays an important role in these systems.

Alternative superconducting qubit designs with improved performance are attracting attention. Here the authors introduce an inductively shunted transmon qubit that offers protection against flux noise and measures quantum tunneling between fluxon states that are shown to be stable for hours.

The ability to coherently switch a state between two systems is a key requirement for quantum information processing. Such control is now demonstrated by shifting the quantum state of a microwave photon between any one of three superconducting-circuit resonators: in analogy to the classic three cups and a ball game.

Quantum nanophotonics examines the interaction between emitters and light confined at the nanoscale. This Review highlights the experimental progress in the field, explains new light–matter interaction regimes and emphasizes their potential applications in quantum technologies.

Condensed-matter physics meets quantum optics in a study of light–matter interaction in the strong-coupling regime using a two-dimensional electron gas in a high-quality-factor terahertz cavity.

Qubits formed from Andreev bound states in a Josephson junction could have performance advantages over existing superconducting qubits. Here proof-of-principle experiments demonstrate long-range coupling between Andreev-level qubits.

The surface plasmon modes of periodic hole arrays in Ag and Al films enhance by one order of magnitude the conductivity and the carrier mobility of organic semiconducting films deposited on these structures.

Strong quadratic coupling between the motion of a membrane and the energy states of a qubit enables the creation of a non-classical energy-squeezed state in the mechanical oscillator.

Normal-mode splitting in the spectrum of cavity coupled atoms is normally observed in the strong coupling regime. Here the authors demonstrate the existence of avoided crossings in the spectrum of an overdamped system of cavity coupled 87Rb atoms that arise due to dressing-induced transparency.