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Dielectric structures that enhance magnetic emission are key for quantum devices but often suffer from thermal instability. Here, the authors realize a dielectric-free, compact metallic resonator with strong Purcell enhancement, enabling stable room-temperature maser action.

Researchers demonstrate the first room-temperature vortex maser, a compact cubic device that emits structured microwave beams carrying topological singularities and orbital angular momentum, opening new avenues for communications and sensing.

One-way sound propagation has been recently proposed in the context of topological acoustics, but is challenged by introducing uniform media motion. Here, Fleury et al.present a practical scheme to achieve topological propagation by modulating in time the acoustic properties of a lattice of resonators, resembling Floquet topological insulators in condensed matter.

Coherent perfect absorption has been limited to continuous wave operation, restricting its use in dynamic systems. Here, authors demonstrate fast temporal anti-lasing that achieves coherent perfect absorption over ultrashort timescales by using topological transitions in hysteretic scattering systems.

Any typical sensing device must absorb energy, thereby altering the measured signal as it propagates on. By exploiting parity-time symmetry via non-Foster circuits, Fleury et al. show that a sensor can be built that absorbs incoming signals without perturbing them or creating a shadow, rendering it invisible.

Here the authors experimentally demonstrate the anomalous and Chern topological phases in a hyperbolic non-reciprocal scattering network, establishing unidirectional channels to induce new and exciting wave transport properties in curved spaces.

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.

A real–momentum topological photonic crystal that harnesses real-space disorder is used to generate a Pancharatnam–Berry phase while preserving momentum-space topology.

Topological localization of photons in both space and time has now been experimentally realized through synthetic photonic quantum walks, enabled by non-Hermitian gain–loss modulations. This investigation into time and space-time topology reveals unique phenomena beyond conventional spatial topological effects, including causality-suppressed coupling.

Non-reciprocal scattering based on linear wave-mode coupling generally suffers from dissipative losses. Here, the authors show how such losses can be compensated by exploiting the synchronization with a limit cycle. Acoustic scattering experiments demonstrate non-reciprocal transmission of audible sound with full immunity against losses.

Although manipulation of objects using light and sound waves is an established technique, it has so far been confined to static environments. Iterative tailoring of acoustic far fields now allows control of objects in disordered and dynamic media.

Existing classical wave analogues of topological insulator are physically wavelength scaled, limiting potential applications. Here, Yveset al. show complex topological crystalline properties in spatially ordered metamaterials with deep subwavelength resonant elements on specific lattices.

Broken and tailored symmetries have a fundamental role in wave phenomena and their applications. This Review surveys the recent progress in the domain of artificial phononic media with an emphasis on the role of symmetry breaking, in both space and time, for advanced wave phenomena.

Wave-based analog signal processing has been challenging for complex nonlinear operations such as data forecasting or classification. The authors propose here an analog neuromorphic platform for optical wave-based machine learning characterized by energy efficiency, speed and scalability.

The physics of oriented topological graphs produces anomalous non-reciprocal topological edge states that have greater robustness to disorder and defects than the best performers at present: namely, Chern states.

Methods to train physical neural networks, such as backpropagation-based and backpropagation-free approaches, are explored to allow scaling up of artificial intelligence models far beyond present small-scale laboratory demonstrations, potentially enhancing computational efficiency.

Analog signal processors could potentially offer faster operation and lower power consumption than digital versions, but are not yet commonly used for large scale applications due to considerable observational errors. Here, the authors demonstrate the unique relevance of topological insulators for improving reliability in such analog processors.

Perfect transmission of sound waves through a strongly disordered environment is demonstrated using a set of speakers that provide exactly the right input to counteract scattering by the disorder. These principles can also be applied to light.

Introducing non-local effects to metamaterials increases the complexity of their dispersion relation, which allows carefully designed elastic structures to mimic the peculiar roton behaviour of correlated quantum superfluids.

Meta-disk utilizes structural multiplexing to significantly enhance optical holographic storage capacity, enabling the storage of numerous high-fidelity images. The technology offers potential applications in optical storage and optical computing.

Reciprocity is a standard characteristic of acoustic wave transmission but breaking the symmetry can lead to greater control and potential applications. Here, the authors report non-reciprocal acoustics by achieving large breaking of reciprocity in sounds composed of harmonics spanning several octaves via non-Hermitian physics.

Controlling audible sound requires inherently broadband and subwavelength acoustic solutions. Exploiting the unique physics of plasmacoustic metalayers, we experimentally demonstrate versatile and tunable sound control over a wide frequency range.

The interplay of topological properties and non-Hermitian symmetry breaking has been implemented for a range of classical-wave systems. Recent advances, challenges and opportunities are reviewed across the different physical platforms.

Clever 3D-printed acoustic materials allow probing a new higher-order semimetallic topological phase using audible sound.

Nonlocality has gained increasing attention in metamaterial and metasurface design. This Review discusses recent advances, focusing on the physical mechanisms of nonlocality that lead to intriguing properties and functions.

Metamaterials provide a platform to leverage optical signals for performing specific-purpose computational tasks with ultra-fast speeds. This Review surveys the basic principles, recent advances and promising future directions for wave-based-metamaterial analogue computing systems.

CRISPR/Cas is a microbial immune system that is known to protect bacteria from virus infection. These authors show that the Streptococcus thermophilus CRISPR/Cas system can prevent both plasmid carriage and phage infection through cleavage of invading double-stranded DNA.

A new thermally latent cocatalyst, based on 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), has been specifically designed for “on-demand” synthesis of polyurethanes in the presence of DBTL as catalyst. This nitrophenyl-based isocyanurate cocatalyst exhibited a low cleavage temperature keeping the system almost inactive at 20 °C and allowing fast polymerization only after increasing temperature up to 60 °C by the release of active DBN.

Nonreciprocal acoustic and elastic wave propagation may enable the creation of devices such as acoustic one-way mirrors, isolators and topological insulators. This Review presents advances in the creation of materials that break reciprocity and realize robust, unidirectional acoustic and elastic wave steering.