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Complex-frequency excitation enables non-Hermitian control on light-matter interactions, without relying on materials gain or loss. Here, authors introduce virtual gain into a whispering-gallery-mode optical microcavity to achieve three amplification regimes, mimicking the dynamics of a laser.

Zihuan Liu and colleagues reported measurements on a MEMS resonator that reaches a mechanical velocity of 50 m/s, a ten-fold improvement over typical devices. These results show that operating MEMS near limits could enable much more sensitive inertial sensors for navigation.

In the layered magnetic semiconductor CrSBr, emergent light–matter hybrids (polaritons) increase the spectral bandwidth of correlations between the magnetic, electronic and optical properties, enabling largely tunable optical responses to applied magnetic fields and magnons.

Exciton energy transfer in monolayer transition metal dichalcogenides is limited to short distances. Here, Shi et al. fabricate a planar metal-oxide-semiconductor structure and show that exciton energy transfer can be extended to tens of microns, mediated by an exciton-surface-plasmon-polariton–exciton conversion mechanism.

Topological order for sound remains largely unexplored. Here, Khanikaevet al. introduce the concept of topological order in classical acoustics, realizing robust topological protection and one-way edge propagation of sound in a suitably designed resonator lattice, thus expanding the ability to tailor acoustic waves.

Time-reversal symmetry breaking opens up new options for magnetic-free integrated photonic non-reciprocal devices. Introducing angular momentum biasing as a form of time-reversal symmetry breaking, Sounas et al. achieve spatiotemporal modulations that give rise to a large non-reciprocal response at subwavelength scales.

The engineering of localized fields is at the base of ultra-compact plasmonic devices. The authors demonstrate that localized plasmon skyrmions provide a unique way to build arbitrarily shaped skyrmionic textures promising high flexibility and robustness for real applications like information processing.

Stable, dissipative optomechanical solitons are realized using optical fields in a whispering gallery mode resonator by balancing the optomechanical nonlinearities with a tailored modal dispersion.

The researchers show that a subwavelength film of indium tin oxide, the bulk permittivity of which is strategically modulated via optical pumping, can be dynamically tuned to act as both a non-resonant amplifier and a perfect absorber. The findings extend the concept of coherent perfect absorption to the temporal domain and may enable coherent manipulation of light in Floquet-engineered complex photonic systems.

Helicity of photons is exploited for preferential emission direction and sorting of valley-polarized excitons is achieved at room temperature.

Nonlinear circuit arrays can exhibit self-induced topological transitions as a function of input intensity and topological immunity against defects and disorder.

Etch-free metasurfaces supporting bound states in the continuum have been used for lasing, although only as passive devices. Here, authors demonstrate highly coherent lasing from an active etch-free metasurface, showing a divergence angle of 0.2⁰, a linewidth of 0.04 nm and coherence time of 20.4 ps.

Observation and control of spin-forbidden dark excitons is demonstrated in a hybrid heterostructure of WSe₂ monolayers and plasmonic nanocavities.

The authors demonstrate an efficient platform for electrically driven reconfigurable metasurfaces by using Ge₂Sb₂Te₅ to realize non-volatile, reversible, multilevel, and fast optical modulation and wavefront engineering in the near-infrared spectral range.

Optical nonlinearity is exploited for non-reciprocal transmission and integrated frequency comb-based optical ranging.

Metasurfaces enable precise tailoring of thermal emission properties. Here, the authors present a corrugated waveguide array design that achieves simultaneous control of polarization and coherence, with record-high temporal, spatial, and spin coherence maintained across broad emission angles.

The authors develop an approach for photonic terahertz phased array without requiring true time delays or integrated electrodes using optically controlled nonlinear metasurface. Programmable 1D and 2D beamforming are realized across 0.8 ~ 1.4 THz.

Shear phenomena in the infrared dielectric response of a monoclinic crystal are shown to unveil a new polariton class termed hyperbolic shear polariton that can emerge in any low-symmetry monoclinic or triclinic system.

The researchers demonstrate orbital-dependent sound-matter interactions in acoustic systems. They unveil duality symmetry and topological phase transitions beyond the conventional SSH model expanding the fundamental understanding of sound-matter interaction.

The authors combine the strong confinement of hyperbolic polaritons with leaky nano-waveguides to demonstrate directional in-plane emission of fast phonon polaritons and their acceleration and deceleration by tailoring waveguide dispersion.

Bias-free optical metasurfaces with a large non-reciprocal response for free-space radiation are discussed, based on thermo-optic nonlinearities. These ultrathin devices may lead to new approaches for areas ranging from signal processing to protection of high-power laser cavities.

By using a resonant sensor to couple two radio-frequency parametric oscillators behaving as Ising spins, a passive wireless device can implement programmable temperature threshold sensing.

Kerr optical nonlinearities are known to be well suited for achieving optical isolation, but the fact that the degree of non-reciprocity is signal-level dependent brings new opportunities as well as limitations.

In the quest for on-chip optical isolation, scientists demonstrate non-reciprocal optical response based on a 'synthetic' magnetic field in an all-silicon platform. This may open directions to optical routing, on-chip lasers and integrated nanophotonic signal processing.

Metasurfaces can solve Fredholm integral equations of the second kind for free-space radiation at optical wavelengths. To this end, an inverse-designed metagrating is coupled to a semitransparent mirror providing feedback to perform an analogue version of the Neumann series.

All-optical image processing using metasurfaces is advancing due to its high speed, integrability, and low energy consumption, yet background noise and clutter hinder the progress. In this work, a real-time optical image processor is introduced, using a metal-dielectric-metal film to perform spatial band-pass filtering in momentum space enabling high-resolution edge detection and real-time dynamic denoising.

Using pump-power-dependent exciton absorption spectroscopy, the authors reveal magnon-mediated exciton–exciton interactions and a consequent nonlinear optical response in CrSBr, an antiferromagnetic semiconductor.

Hyperbolic shear polaritons (HShPs) are strongly confined light-matter excitations that have been previously observed in low-symmetry 3D materials with limited tunability. Here, the authors report the observation and manipulation of HShPs in twisted bilayers α-MoO₃ by tuning the sample structure or using a graphene electrostatic gate.

Moiré quasicrystals exhibit many exotic phenomena. Here, the authors report an acoustic moiré quasicrystal that not only achieves a localization-delocalization transition, but also enables wave propagation shifting from diffusion to canalization or localization.

Communication systems require non-reciprocal electromagnetic propagation, which is difficult to realize in circuits. An alternative is demonstrated by modulating the phase of strongly coupled resonators in a circular configuration.

Optical-frequency antennas efficiently couple light into very small volumes. Introducing an important concept from radiofrequency antenna design, that of loading with so-called lumped circuit elements, may provide a way of tuning the frequency response of optical nanoantennas.

Suitably engineered mechanical metamaterials show static non-reciprocity—that is, the transmission of motion from one side to the other depends on the direction of that motion.

Small asymmetries in a 2 × 2 array of nanoparticles enable the experimental observation of a magnetic-based Fano resonance at optical frequencies.

Lumped elements such as resistors, capacitors and inductors play a crucial role in electronic circuits. Now, inspired by metamaterials technology, the experimental realization of lumped circuit elements for optical frequencies provides a standardized platform for applications such as mixing and multiplexing of optical signals.

Previous predictions that light radiated by modes around a bound state in the continuum (BIC) condition should exhibit a vortex in the far-field polarization profile are experimentally confirmed. The findings shed light on the origin of BICs.

Researchers demonstrate that image-processing metasurfaces can be dynamically reconfigured by using phase-change materials. The work might lead to novel tunable devices for compact optical computing for applications in AR/VR and bio-medical imaging.

Resonance-based systems such as electroacoustic transducers are often limited by narrow bandwidth. Here, authors report a digital non-Foster inspired circuit demonstrating significant bandwidth and power level enhancement with greater reconfigurability than conventional analog non-Foster approaches.

In the past decade, artificial materials with unusual wave interactions have significantly evolved and matured. In honour of the tenth anniversary of the premiere metamaterials conference, we look at the directions in which this field is evolving, and its impact on technology.

Van der Waals NbOCl2 crystal is a candidate platform for subwavelength thin film photon-pair sources. Here, the authors demonstrate generation of polarization entangled states from a two-layer stack of orthogonally oriented van der Waals crystal.

Free-space meta-optics with ultrahigh quality(Q)-factor at visible wavelengths is demanded but very challenging to achieve due to the fabrication imperfections. Here, the authors design an etch-free metasurface with minimized fabrication defects and experimentally demonstrate a million-Q resonance at 779 nm wavelength.

Natural and engineered Poisson’s ratios obey fundamental bounds determined by stability, linearity, and thermodynamics. Here, the authors design and realize self-bridging metamaterials with Poisson’s ratios surpassing the theoretical bounds.

Here, the authors demonstrate that dark excitons in two-dimensional transition metal dichalcogenides can diffuse over several micrometers, and prove that this repulsion-driven propagation is robust across non-uniform samples.

A metasurface is used to generalize the Rashba effect from circular polarizations to any polarization state for thermal emission.

Topological traps and guides for polaritons expand the potential for light-matter wave manipulation in ultrathin materials, facilitating photonic on-chip integration. Here the authors demonstrate a chiral-defect cavity in a planar metasurface that efficiently trap mid-IR phonon-polaritons in topological defects.

Polarization control is of paramount importance for various applications. Here, the authors enable extreme control over light polarization spanning the entire Poincaré sphere by combining coherent control of wave phenomena and the physics of bound states in the continuum.