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Systems with strong photon-photon interactions enable advanced quantum optical applications as well as the study of highly correlated light-matter states. Here the authors report strong coupling between single- and two-photon states in a superconducting circuit, enabling a new regime of nonlinear quantum optics.

Nonreciprocal quantum effects can unlock unique quantum resources but unidirectional quantum synchronization has been overlooked. Here authors demonstrate robust one-way quantum synchronization of phonons, overcoming imperfections and noise via combined Sagnac and magnon Kerr effects.

The effect of spin on the trajectories of polarized light beams has now been experimentally observed, with results that agree with the predictions of Berry phase theory.

This study demonstrates dark-mode engineering as a powerful tool to achieve switchable topological phonon transfer and blockade, offering a versatile approach to robust, scalable phononic control for quantum information processing.

Landau states are associated with the quantised orbits of charged particles in magnetic fields. By manipulating electron vortex beams in a magnetic field, this study reconstructs the internal quantum dynamics of free-electron Landau states, which differs strongly from the classical cyclotron rotation.

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.

Researchers demonstrate chaos transfer between two optical fields in an optomechanical system.

It is now shown that coupled optical microcavities bear all the hallmarks of parity–time symmetry; that is, the system’s dynamics are unchanged by both time-reversal and mirror transformations. The resonant nature of microcavities results in unusual effects not seen in previous photonic analogues of parity–time-symmetric systems: for example, light travelling in one direction is resonantly enhanced but there are no resonance peaks going the other way.

Chirality-induced quantum non-reciprocity of cross-channel correlations is demonstrated in a rubidium vapour system by flipping the flow direction of one of the circularly polarized laser beams. It can be extended to multicolour sidebands with Floquet engineering.

The full description of exceptional points in the non-Markovian regime is complicated by the unclear applicability of standard techniques such as spectral analysis. Here, the authors fill this gap by proposing a general framework that combines the pseudomode equation of motion and the hierarchical equations of motion.

Moderate disorder can induce topologically nontrivial phases. Liu et al. report the experimental observations of the competition and interplay between Thouless pumping and disorder on a 41-qubit superconducting quantum processor.

The authors observe an exceptional point and the corresponding phase transition in a superconducting non-Hermitian circuit. They find non-reciprocal microwave transmission can be achieved within the broken symmetry phase in the few-photon regime.

One-way propagation of light through a standard telecommunications fibre is demonstrated by coupling the fibre to a rapidly rotating silica-glass sphere.

Linewidth broadening of a phonon laser operated at an exceptional point of a compound optomechanical system is experimentally demonstrated.

Sufficient optical gain provided by Yb³⁺ doping allows phonon lasing from a levitated optomechanical system at the microscale, which exhibits strong mechanical amplitudes and nonlinear mechanical harmonics above the lasing threshold.

Mode locking, which is a common technique to produce short laser pulses, is demonstrated in a topological laser.

The authors report a controllable third-order cusp singularity in the phase-tracked closed-loop oscillation of two coupled mechanical modes. This finding addresses the challenge of constructing and controlling higher-order singularities.

Most theoretical studies of open quantum systems make several simplifying approximations but experimental devices, and some natural systems, now operate in regimes where those methods break down. Lambert et al. introduce a tractable approach to the spin-boson model without relying on the Born, Markovian and rotating wave approximations.

This works explores the interplay between nonlinearity and non-Hermitian skin effect in reshaping topological modes at the interface between Hermitian and non-Hermitian lattices. It is shown that this interplay yields fully delocalized and reconfigurable topological modes without fine parameter tuning, while facilitating stable long-range patterns through external pumping.

Quantum simulations of topological matter with superconducting qubits have been attracting attention recently. Xiang et al. realize 2D and bilayer Chern insulators with synthetic dimensions on a programmable 30-qubit-ladder superconducting processor, showing bulk-boundary correspondence.

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.

Inspired by ideas and techniques for cooling atomic gases, an experiment demonstrates how the temperature of micrometre-scale electronic devices can be lowered using solid-state quantum circuits.

Giant Rydberg excitons reveal signatures of quantum chaotic behaviour in the presence of time-reversal symmetry breaking enforced by the background solid-state lattice, and they provide a new mesoscopic platform for fundamental studies of quantum chaos.

Charged particles influenced by electromagnetic fields, even when the two never touch? Surely, it can only be quantum physics. But surprisingly, the quantum nature of this particular effect has been disputed.

Encircling exceptional points (EPs) is of great significance in studying topological properties in non-Hermitian systems; however, non-adiabatic transitions pose a major challenge to the continuous dynamically encircling of EPs. This work presents a scheme for the dynamically encircling of EPs through phase-tracked closed-loop control, enabling the smooth evolution along the eigenfrequency Riemann surface.

In this work, the authors show that photonic topological lattices with dissipative couplings could exhibit non-Abelian dynamics and geometric phases that are in sharp contrast to those arising in typical energy-conserving systems.

By exploiting unique properties of both diabolic and exceptional points in the spectrum of non-Hermitian systems, the authors propose an experimental scheme of a programmable multimode switch, which opens alternative routes for light manipulations.

Atoms lose coherence via interactions with each other and the walls of their environment, which degrades the performance of atomic systems. As a route to minimize such effects, Okaba et al.use kagome-lattice hollow-core photonic crystal fibres to confine atoms, preventing them interacting with the wall.

Optical analogues of electromagnetically induced transparency and Autler–Townes splitting originate from different mechanisms but both are quantified by a transparency window. Here, Peng et al.use the Akaike information criterion to discriminate between the two regimes in coupled whispering gallery mode microresonators.

The momentum and spin of a propagating photon are given by its wave vector and circular polarization, respectively. Bliokh et al.here show that evanescent electromagnetic waves possess a polarization-dependent momentum component and a polarization-independent spin component, which are both orthogonal to the wave vector.

Nanoscale engineering can now take advantage of a new ratchet device: it acts as a diode for superconducting vortices, but its directionality can be controlled and repeatedly reversed to become an effective 'two-way street'.

Topological phenomena have mostly been studied in conservative systems. Experiments on optical resonator networks now show that topologically non-trivial characteristics can also emerge in dissipation.

One way to describe a particle is as a localised, 3-dimensional topological state, such as a skyrmion or hopfion. Here, the authors demonstrate and characterise particle-like skyrmionic hopfions in a free-space structured light beam.

Quantum Rabi model is a standard tool for describing cavity quantum electrodynamics, but the potential shortcomings of its single-mode version are usually neglected. Here, the authors show that, in the ultrastrong coupling regime, a multimode Rabi model is mandatory in order to avoid unphysical results.

Electromagnetic surface waves, derived from Maxwell theory, underpin many optical effects and applications. Here, Bliokh et al. show that surface waves at interfaces between isotropic media have a topological origin described by the non-Hermitian helicity operator and bulk-boundary correspondence.

Superconducting giant atoms are realized in a waveguide by coupling small atoms to the waveguide at multiple discrete locations, producing tunable atom–waveguide coupling and enabling decoherence-free interactions.

The presence of processes that cannot be simulated classically in open quantum system dynamics is acknowledged, but an exact quantifier for this non-classical character is still missing. Here, the authors provide a quantitative measure of non-classicality for purely dephasing evolutions.

Li et al. show that human value-based decision-making can be modelled using the quantum reinforcement learning framework. These new models reveal the importance of the medial frontal cortex in this quantum-like decision-making process.