A new solvable model of interacting quantum particles exhibits a broader range of dynamical behavior than previous models, which could provide experimentalists with better insight into mixed-mass ensembles of particles.

Next-generation wireless communication networks will require powerful, stable sources of electromagnetic radiation operating at terahertz frequencies. A new study demonstrates the feasibility of such a source by combing a microscale cavity with a photomixer.

Laser-matter collisions can generate flashes of energetic particles, but attempts to create high-energy photon sources from such interactions quickly run into limitations on energy. New results show how to exploit fundamental physical processes, such as the creation of antimatter from light, to overcome these limits and create an efficient, ultrabright source of giga-electron-volt photons, with capabilities far surpassing those of other sources.

Understanding the physical properties of Fermi superfluids is a key step toward the development of high-temperature superconductors as well as insight into the inner workings of neutron stars. New experiments reveal the first comprehensive measurements of thermodynamic properties of fermions in a superfluid with enough accuracy to compare models for how these particles interact.

Understanding the flow of complex fluids through confined spaces, and forces governing the flow, is key to diverse fields, from blood flow to lubricant design. But studying such situations is difficult because typical devices can’t achieve the necessary degree of confinement. New experiments and simulations reveal flow behavior under different levels of confinement and show how this behavior can be tuned.

Different complex systems can exhibit remarkably similar behavior, a concept known as universality. Defining different classes of universality for driven nonequilibrium systems, however, is difficult. A new analysis shows how one of these classes—the Kardar-Parisi-Zhang class—can be experimentally realized using a fluid of exciton-polaritons and how the universal behavior can be changed by making this system strongly anisotropic.

A theoretical model of light spreading and scattering improves accuracy precision of position and size measurements made with an optical microscope by as much as 100 times.

Spatial dimensionality of a system determines the types of phenomena it can exhibit. A new analysis shows how the dimensionality of a single spin-1/2 particle can be effectively increased by applying a drive with two incommensurate frequencies, thereby dynamically inducing an exotic topological phase of matter.

Quantum metrology is a technique for using principles of quantum theory to make ultraprecise measurements of physical systems, however, its effectiveness is frequently hampered by environmental noise. A new theoretical analysis provides criteria for knowing whether noise will impact a measurement and if corrections are possible.

Engineering a strong interaction between a single photon and emitter could lead to novel quantum optical devices but generally requires confining the light inside a cavity. New experiments get around this requirement by coupling a few photons to a single superatom—thousands of atoms behaving as a single entity.

Electron-spin-resonance measurements can achieve greater sensitivity using squeezed light as an input.

Quantum simulation offers a powerful approach to testing quantum field theories (QFTs) via precise manipulation of atomic and molecular experiments that emulate the theories under investigation. A new analysis introduces a protocol for implementing a generating functional, the cornerstone of any QFT, in the lab.

New investigations of a type of high-temperature superconductor using time- and angle-resolved photoemission spectroscopy reveal new details about the nature of photoexcitation and its relation to superconductivity.

The Kibble-Zurek mechanism describes the formation of topological defects in the wake of continuous phase transitions. A new analysis presents a global upgrade to this picture that reveals new phenomena as fluctuations in the system transform from strongly interacting to noninteracting.

Random number generation plays a pivotal role in quantum information applications (such as encryption), but generating random quantum operations requires exceptionally complex resources. A new theoretical analysis shows that an interacting many-body system can blend classical randomness through its dynamics to create quantum randomness.

Dualities help theorists describe complex systems using the language of systems that are easier to understand, but keeping track of symmetries and constructing concrete models is often nontrivial. A new analysis presents exact mappings for dual theories used to describe Dirac fermions in two dimensions.

Resonant tunneling diodes, being the fastest electronic devices to date, operate by relying on one of the most surprising quantum-mechanical effects: tunneling. Taking advantage of this ultrafast process, however, has proven to be difficult within the nitride family of semiconductors. New techniques for growing GaN crystals have now led to unprecedented observations of resonant tunneling physics in nitride quantum devices.

High-temperature superconductors such as cuprates exhibit strange behaviors when they are in a metallic state, for example at temperatures above their critical temperature. A new theoretical analysis of the perovskite iridate Sr${}_2$IrO${}_4$, which shares some properties with cuprates, offers insight into the reason for these behaviors.

Electrons and quasiparticles in solids could be trapped and moved using surface acoustic waves.

Topological crystalline insulators are one of a new class of materials whose surface electronic behavior differs from its interior behavior, although it’s not clear how the internal structure affects the surface and vice versa. New experiments take a close look at these connections in metastable tin selenide, a semiconductor that can exhibit topological behaviors.

Many-body localization is widely assumed to not be compatible with physical systems that exhibit long-range interactions. A new theoretical analysis shows that it is compatible with such systems, thus opening many-body localization physics to a wide range of novel situations.

Despite many advances, rapid, precise 3D tracking of nanoscale particles in a complex environment remains challenging. A new technique based on four-wave mixing interferometry not only precisely tracks a gold nanoparticle but also is sensitive to particle asymmetry and orientation.

Quantum repeaters allow for reliable transmission of quantum information over long distances. One possible approach relies on highly entangled photons. A new protocol provides a way to generate arbitrarily large states of entangled photons using just one emitter coupled to a single qubit.

A key parameter for characterizing disease outbreaks and other types of dynamics on complex networks is the largest eigenvalue of the adjacency matrix. A new analysis presents a very general way of estimating it and a physical interpretation of its value.

Pulsar timing and laser-interferometer gravitational-wave observations are two powerful astronomical tools for testing our understanding of gravity. A new analysis demonstrates the complementarity of these techniques. As new observatories come online in the coming years, combining these measurements could improve constraints on an illustrative class of theories that modify Einstein’s general theory of relativity.

In a Weyl semimetal, the behavior of charge carriers mirrors the physics of Einstein’s special relativity. A new analysis shows how to engineer materials where the particles mimic the principles of general relativity, opening the door to novel electronic devices.

The effectiveness of punishment can be challenged by an unwillingness to shoulder the costs of punishment and by noncooperators who punish cooperators. Simulations based on techniques from statistical physics show how these can cancel one another in an unlikely and counterintuitive evolutionary outcome.

Randomness in the arrangement of molecules within certain types of frustrated magnets may offer a way to promote and stabilize exotic states of matter known as spin liquids. New neutron-scattering experiments characterize the disorder in the spin ice candidate Pr${}_2$Zr${}_2$O${}_7$ and provide an explanation for some of this material’s unique properties.

Changing the geometrical organization of molecules in a liquid crystal can change how objects move within it and how it interacts with light, opening a door to novel applications. New experiments show how to produce a wealth of patterns in cholesteric liquid crystals, revealing also how these materials transition from one pattern to another.

Pulses of x-ray light that last mere attoseconds are essential to capturing fundamental processes in nature, such as the motion of electrons and their role in chemical bonding. New experiments generate and, for the first time, characterize attosecond pulses in the soft-x-ray portion of the spectrum.

Despite the ubiquity of soft adhesives in everyday materials, much of their underlying physics remains unknown. New experiments in which small glass spheres are pulled from a silicone gel reveal crucial differences in how soft and stiff materials adhere.

While the edge states of a 2D electron gas in the fractional quantum Hall regime have many fascinating properties, the bulk dynamics are widely assumed to be uninteresting. A new theory reveals not only rich behavior in the bulk but also a unified framework for deriving known properties of this state.

The third law of thermodynamics dictates that it is impossible to cool anything to absolute zero in a finite amount of time and with finite resources, but the law lacks a quantitative formulation to express the limits of what is allowed. A new analysis introduces such a formulation, which quantifies how close to zero a system can get given some initial amount of energy.

An analysis of spin-precession data of atoms and neutrons sets some of the tightest limits to date on the strength of interactions between axions and gluons or nucleons.

Describing three bodies moving under known mutual forces is difficult, especially in quantum mechanics. On the other hand, the two-body problem is very simple. A new method uses the two-body solution to solve this three-body problem.

Advances in quantum optics and quantum information technologies increasingly require a way to fully understand the state of single indistinguishable photons. While previous approaches have needed two or more measurements, a new experiment demonstrates a way to characterize single-photon states with just one measurement.

Living cells depend on molecular motor proteins to transport cargo, but crowding effects are thought to impact transport efficiency. A new imaging technique reveals motor behavior under crowding conditions, elucidating the physical nature of how these molecules respond to cellular traffic.

In flow channels, the fluid is expected to transport suspended particles unless the particles are too large or adhesive. New experiments show unexpected behavior—an accumulation of particles at flow junctions—when solutes are dissolved in the fluid.

Polymer additives in simple fluids help reduce flow resistance and are an enormous benefit in many industrial and biomedical applications, but they are challenging to study. New visualization techniques reveal how incremental polymer additions to water-based solvents affect the development of a single vortex in the fluid.

Intervalley plasmons are a novel type of collective excitation observed in monolayer transition-metal dichalcogenides (TMDs). A new analysis reveals why a particular optical signature of these excitations shows up in certain electron-doped TMDs.

Electron spectroscopy and electron transport experiments are key techniques to probing the electronic structure of topological insulators, but results from these two methods disagree. A new analysis shows that the problem is inherent to ultraviolet light used in electron spectroscopy, and offers a solution.

Berry phase—a parameter that provides deep geometric insight into quantum mechanical systems—is difficult to measure in condensed-matter systems. New experiments and theoretical analyses demonstrate a path to such measurements by observing sidebands of infrared light transmitted through driven, thin layers of a semiconductor.

A device that routes microwave signals could help researchers scale up quantum-computing architectures.

The relationship between the structure and dynamics of a network is key to understanding the behavior of complex systems. A new analysis shows how network optimization, whether designed or evolved, can lead to collective dynamics that depend sensitively on the structure of the network.

Magnetic Skyrmions are topologically protected spin structures that have emerged as attractive candidates for magnetic storage applications. A new analysis goes beyond the traditional classical equations that describe Skyrmion dynamics, providing a full quantum description of the propagation of Skyrmions in insulating magnetic films at zero and finite temperatures.

In gauge theories with one spatial and time dimension, the gauge degrees of freedom are not independent and can be integrated out, making them simpler to work with. A new analysis extends this to an explicit formulation of the physical subspace for a $(1+1)$-dimensional SU(2) lattice gauge theory.

While many-body localization is well understood in one-dimensional systems, its behavior in two or more dimensions is largely unknown. New experiments hint at a many-body localized phase in a two-dimensional system and provide insight into how a system transitions between this phase and a normal thermal phase.

New theoretical constructions describe a largely unexplored phase of matter, a type of strongly interacting gapless topological quantum system. Such a framework could lead to a more thorough study of various exotic quantum materials.

Wave excitations (magnons) along the helical arrangement of magnetic moments in helimagnets generally travel along this helix, while orthogonal magnons are thought to require much higher energy. New experiments reveal the existence of low-energy orthogonal magnons that could lead to a new understanding of a broad class of magnetic materials.

Random numbers are at the heart of secure communication protocols; unfortunately current hardware-based approaches for their generation suffer from a number of problems. A new experiment demonstrates a laser-based approach to random-number generation that circumvents technical influences that might spoil the randomness in the generated numbers.

Self-trapped wave packets known as solitons have been observed in one and two spatiotemporal dimensions, but three-dimensional solitons have remained elusive. A new experiment demonstrates the first observation of a train of three-dimensional optical solitons, also known as light bullets.

Quantum computing could greatly speed up machine learning techniques that rely on sampling complex probability distributions, but limitations prevent demonstrations of feasibility. A new technique implemented on a quantum annealer surpasses these limitations and shows how quantum computing can assist in machine learning tasks.

Multimode optical fibers offer more transmission capacity by supporting multiple transverse modes, but crosstalk between these channels remains a vexing problem. New experiments and theoretical analysis reveal unique light states in multimode fibers that are strongly protected against this crosstalk.

Recent experiments have shown that the transition-metal dichalcogenide 1T-TaS${}_{2-x}$Se${}_x$ can transition from a Mott insulator to a superconductor by varying the S/Se ratio. New measurements with a scanning tunneling microscope along with first-principles calculations reveal the mechanism underlying this transition.

Optical frequency combs, which constitute equally spaced frequency lines, can be generated using temporal dissipative Kerr solitons—stable laser pulses generated in a laser-driven nonlinear microresonator—but these solitons can destabilize and oscillate. A new analysis reveals a novel mechanism that can trigger “soliton breathing,” highlighting the rich nonlinear dynamics of dissipative temporal structures in microresonators and identifying a regime that has to be avoided in applications.

Researchers have demonstrated a device that can project two distinct holographic images when illuminated at different angles.

Spin ice is an exotic phase of low-temperature magnetic material in which the atoms behave like a liquid no matter how cold it becomes. New computer simulations look at how spin ice behaves near absolute zero and find surprisingly rich behavior.

Now that gravitational-wave detection is a reality, measurements of gravitational-wave polarization could provide crucial tests of alternatives to the general theory of relativity. A new analysis provides a way to extract polarizations from the stochastic gravitational-wave background and investigates how additional detectors could provide constraints on theories of gravity.

The study of surface phonons, collective atomic vibrations localized on the surface of solids, has long been helped by insights from experiments on surface plasmons, their electronic counterparts. A new analysis takes these analogies in the opposite direction, using modern concepts for plasmons to explain current phonon experiments.

Artificial materials that increase their volume when subject to an increase in air pressure—contrary to expectations—could prove useful in artificial muscles and actuators. New experiments demonstrate, for the first time, the successful fabrication and performance of such an unusual material.

As small prototype quantum processors progress to large-scale, fault-tolerant computers, it is increasingly necessary to quantitatively assess the performance of quantum error correction. A new benchmark offers just such an assessment of trapped-ion quantum processors.

Topological materials hold much promise for quantum computers that are highly tolerant to errors, but the information can be corrupted by thermally excited quasiparticles. New numerical simulations show that in some materials, quantum information can be protected for much longer than expected.

Quantum annealing is an approach to quantum computing that could offer fast, efficient solutions to certain types of complex problems. New experiments take an important step toward implementing a cold-atom-based quantum annealer that relies on coherent many-body interactions between Rydberg states in cold atomic gases.

Experimental observations of the rate at which crystalline grains grow in polycrystalline materials often differ markedly from theoretical predictions. New experiments reveal the physical mechanism that determines this rate and lead to robust theoretical expressions that describe how grains grow.

Stokes’ law states that the friction coefficient of an object in a solvent does not depend on an external confining potential, but this assumption turns out not to be true. New simulations show that a methane molecule in water experiences a significant increase in its friction coefficient, a finding which has wide ranging implications for understanding molecular dynamics in solvents.

Charge-density waves (CDWs) in the normal state of cuprates could shed light on the physics of their high-temperature superconductivity. New experiments, however, show no evidence for such waves in an electron-doped cuprate, which means the universality of CDWs in cuprates has yet to be confirmed.

Half-metals such as chromium dioxide behave as metals in one spin orientation and insulators or semiconductors in the opposite one. New measurements of the electronic structure of CrO${}_2$ provide clear insight, for the first time, into the role that electronic correlations play in affecting this behavior.

Landau levels, the quantization of cyclotron orbits of electrons in a magnetic field, can give rise to a rich array of behaviors in materials. A new analysis reveals a new type of state that breaks inversion symmetry and arises when a few Landau levels have nearly the same energy.

The celebrated “tenfold way” provides a scheme for categorizing general topological states of matter, but it does not take into account the crystal symmetries that always exist in real materials. A new method extends this organization to allow the categorization of all topologically distinct electronic band structures in materials with only crystal symmetries for any number of physically relevant dimensions.

Self-deploying materials based on principles of origami have many potential technological uses, but can be limited by hidden complexities in their folding behavior. A new analysis explores these limits and offers strategies for avoiding these undesired traps.

Highly variable, perpetual activity in the brain is thought to arise from the cortex operating close to a phase transition. New theoretical models propose a more general scenario: changes in neural dynamics unfold according to neutral drift, guided by stochastic effects.

Spin waves traveling in certain directions within antiferromagnetic materials appear to be unstable and likely to split up into spinons. New simulations show that, actually, these abnormal spin waves aren’t unstable, but rather fluctuate between spin waves and spinons.

While there are many explanations for the variety of material surface states, which can reveal interesting surface details and bulk properties, researchers lack an understanding of how these states arise in nonsymmorphic square-net semimetals. New experiments and calculations reveal that surface states in the compound ZrSiS come about because of nonsymmorphic symmetry breaking at the surface.