Not much is known about what shapes of molecules lead to an $x$-atic phase, an exotic phase of two-dimensional matter that shares properties of both fluids and solids. A new set of simulations investigates the behavior of a range of polygon-shaped particles and shows how body symmetry influences these phase transitions.

Brownian motion—the random movement of microscopic particles in a fluid—usually gives rise to a Gaussian probability of finding a particle at a particular place at a specific time. But in some situations, this probability behaves differently. A new mathematical model shows how to reconcile this behavior with other hallmarks of Brownian motion.

Nanomachines are subject to random thermal and quantum fluctuations that are not captured by traditional thermodynamic theory. A new theoretical investigation offers a step toward a unified nanoscale theory by showing how externally prepared systems (e.g., atoms in an optical cavity or DNA bases in an enzyme reaction) that interact with a nanoscopic device can be a source of nonequilbrium free energy.

Both computers and living cells copy information, but doing so comes at a cost of energy. A new theoretical analysis shows that biological systems come close to but do not reach the predicted lower bound on this energy, and that the cost increases as copying becomes more accurate.

Nonlocal correlations—correlations among atomic particles that cannot be described classically and that are stronger than those accounted for by entanglement—are of fundamental interest to physicists, but remain difficult to characterize in many-body systems. A new theoretical analysis shows that the ground states of spin Hamiltonians in some systems can exhibit nonlocal correlations.

Methods for generating quantum pseudorandomness are essential to understanding randomness in many quantum phenomena, but have not been fully explored. A new analysis shows that quantum pseudorandomness can appear spontaneously in certain many-body systems, leading to a prescription for developing quantum circuits that generate pseudorandomness.

Active matter systems, composed of individual agents that use energy to self-propel, operate far from thermal equilibrium. But markers of nonequilibrium at macroscopic scales are often elusive. A new theoretical analysis shows how to diagnose large-scale breakdowns in time-reversal symmetry, which is a key property of nonequilibrium.

Ultraprecise measurements of displacement and force can run into a limit on precision due to random forces imparted by the photons used for the measurement. An investigation into a technique for modifying the readout of an interferometer to avoid these limits demonstrates sensitivity improvements.

Magnetization waves (or spin waves) are an intriguing alternative to charge currents in computation and data processing. A new experiment shows how a series of ultrashort laser pulses can be used to generate spin waves, a method that has many advantages over conventional means.

Strange metals, which exhibit unusual changes in physical properties such as electrical resistance and heat capacity in response to temperature, are difficult to understand with current theoretical tools. A new analysis provides the exact solution to a theory that describes two-dimensional strange metals that arise as a metal transitions to a magnet.

Majorana particles, which are their own antiparticles, offer great potential for future quantum computers, but significant experimental challenges hamper proof of their existence and properties. New measurements of electrical supercurrents in an HgTe quantum well provide a way to gain insight into the induced superconductivity required for these experiments.

Quantum systems that are far from equilibrium can exhibit strange behavior, such as the emergence of coherence in an expanding Bose gas in an optical lattice. A theoretical analysis provides new insight into this phenomenon and a toolkit for understanding a wide range of similar phenomena.

Some quantum systems can enter a many-body localized (MBL) phase, where the particles do not settle into thermal equilibrium but remain stuck in some initial state. A new theoretical analysis explores the transition between MBL and thermal phases and finds that the transition is driven by the growth of a network of quantum entanglement.

Efficient interactions between photons and atoms are an essential ingredient for future quantum networks. A new experiment uses an optical resonator to create enhanced coupling between light and a single organic dye molecule.

Driving a quantum liquid—by subjecting it to some external force—can generate exotic phases of matter, but such phases are unstable. A suite of mathematical methods reveals the origins of these instabilities and identifies physical manifestations that can be observed in current experiments.

Understanding the behavior of electrons in semiconducting nanowires is hindered by difficulties in probing these delicate structures. Development of a portable chamber, which keeps the nanowires under ultrahigh vacuum from growth to measurement, allows for the first thorough study of electron phase coherence in a semiconducting nanowire.

High harmonic generation can produce attosecond-long pulses of light, which are a useful probe of physical processes that require extremely high time resolution. A new mathematical analysis shows how electron delocalization contributes to this emission in a solid.

Many-body-localized (MBL) phases are an intriguing state of matter where quantum systems fail to thermalize and retain their initial conditions for an indefinite amount of time. A new proposal for how to mathematically encode the dynamics of large, one-dimensional MBL systems shows an exponential decrease in computational time for analyzing the energy spectrum.

Cubically dispersed Dirac fermions are proposed exotic quasiparticles that have no analog in the standard model of particle physics, and they have not yet been identified in any compound. A design methodology quickly identifies one group of compounds as an ideal candidate and shows promise for realizing other novel types of fermions.

When an ensemble of atoms interacts with an environment, it’s possible that two steady states can coexist—a bistable state. A new experiment investigates this possibility in a sample of Rydberg atoms and finds that, in large systems, many excitations exist that are incompatible with a bistable state.

Machine learning has recently gained attention as a possible way to understand phase transitions in many-body quantum systems. A new entanglement analysis reveals crucial properties of the data structures that encode quantum states in a neural network, opening new inroads in applying machine learning to quantum many-body physics.

Deep theoretical links may exist between how space encodes information and error correcting codes being developed for quantum computers. A new analysis explores these connections further and offers insights into not just error-correction codes but also how we interpret ideas about spacetime.

Magnetic monopoles have been sought for decades but never definitively observed. Recent experiments have created different analogs of monopoles in Bose-Einstein condensates, including quantum-mechanical and Dirac monopoles. Now a new experiment in this system shows how a quantum-mechanical monopole can evolve into a Dirac monopole.

Phonon transport—the movement of vibrational wave packets in a solid—in nanostructures is a key element in controlling solid heat conduction, but it remains a complex design challenge. A new framework uses informatics and phonon transport calculations to greatly accelerate the design process and reveals nonintuitive structures that are more effective than their traditional counterparts.

The ultimate goal of research on iron-based superconductors, which are promising candidates for high-temperature applications, is the development of a robust theory that describes their behavior at the microscopic level. New experiments with FeSe reveal that strong coupling between the spin and orbit of electrons is an essential ingredient to any such theory.

Transition-metal dichalcogenides are a class of two-dimensional materials that offer potential for developing flat and flexible transistors and optoelectronics, but their quality is often hindered by traditional methods for depositing these atomically flat materials. An experiment demonstrates a new technique that leads to higher quality crystals and better access to studying their properties.

Variational quantum algorithms (VQAs) mix quantum machines with classical optimizers to solve complex computational problems. A new analysis reveals the optimal method for implementing a VQA, which could lead to improvements in future quantum computing techniques.

Crystals with rare-earth ions could lead to quantum repeaters that enable secure quantum communications over long distances.

Error correction is essential to the development of practical quantum computers, but a leading method that relies on “surface codes” requires distinct and seemingly incompatible approaches to different computational operations. A new framework unifies these schemes and shows how to combine and compare different codes, an important tool for universal quantum computation.

Some crystalline materials show indirect evidence of glasslike behavior, which is surprising because a crystal is highly ordered whereas a glass is not. By using colloidal crystals composed of micrometer-sized spheres suspended in water, a new experiment mimics such phenomena and provides a novel way of understanding this behavior.

Understanding interactions between filamentary structures could offer important insights into the dynamics of a wide range of physical systems. A new imaging technique reveals novel vortex filament interactions in a Bose-Einstein condensate (BEC) and helps establish BECs as a powerful laboratory for investigating filament dynamics.

The search for topological superconductors—superconductors where the bulk accommodates only electron pairs while the surface also allows for motion of single electrons—largely relies on tweaking environmental knobs to create the desired characteristics. A proposed experimental setup uses the phase difference between two superconductors to create a topological phase.

The fractional quantum Hall effect, where a 2D electron gas exhibits quantized electrical conductance, lies at the heart of proposals for practical quantum computing, but it has never been seen in ultracold atomic gases, which could offer impressive control of quantum states. A new analysis shows how a 1D analog could appear in several experimental frameworks.

Sound diffusers are widely used to improve acoustics in a space, but the size of traditional diffusers limits their usefulness at low- to mid-range frequencies. New experiments show that a prototype diffuser based on acoustic metasurfaces performs on par with conventional designs despite being roughly 1 order of magnitude thinner.

Scattering matrices are a key mathematical tool used by physicists to understand how the output and input of many types of systems relate to one another. A new analysis shows how a scattering matrix can be determined solely based on quasinormal modes, providing an effective and powerful tool for gaining insight into complex physical systems.

The air gap between a droplet and a smooth surface can drain up to 1000 times faster than theory predicts, a discrepancy that impacts many industrial processes. A new experimental investigation solves this mystery by showing how environmental influences and minute boundary velocities can speed up contact.

How a relatively simple gene made of DNA encodes the complex structure of a protein is an open question. A new mathematical model suggests that DNA codes for the large-scale motion of a protein in just a few parameters.

A trapped ion excited to a hydrogen-like Rydberg state shows promise for qubit applications.

Computer simulations of supercooled liquids being cooled below the glass transition temperature are unable to capture the enormous dynamical range present during the transition, hindering studies of this transformation. For the first time, new computational models and optimized Monte Carlo algorithms close this gap and even go beyond experimental capabilities.

Fractal geometry is inherent to chaotic systems, but this is not well understood in undriven dissipative processes, in which chaos necessarily vanishes over time. A new analysis leads to a novel framework for studying these systems and shows, for the first time, that they too can generically exhibit fractal behavior.

The ability to control matter at the quantum level is essential for many applications. A new analysis shows that an exotic state known as a squeezed vacuum can provide unprecedented control over interactions between quantum entities.

Quantum entanglement lies at the heart of proposals for encoding and manipulating information in a quantum computer, but detecting its presence in large ensembles of particles remains challenging. A new technique for entanglement detection promises to be both computationally and experimentally efficient in systems involving tens of particles.

FERMI is a novel class of free-electron laser that is capable of producing femtosecond pulses of ultraviolet and x-ray light, essential to studying ultrafast processes in matter. A new investigation characterizes FERMI’s pulse shape and confirms that it routinely generates Gaussian pulses lasting a few tens of femtoseconds.

Raman scattering could contaminate astronomical observations that use “laser guide stars” to correct for the effect of atmospheric turbulence.

Bimodal microlasers have recently gained interest for potential applications in optical memories, tunable switches, and as a platform for studying nonequilibrium phase transitions. A new investigation reveals not only the underlying mechanisms that controls mode switching in these devices but also that this switching corresponds to a transition from lasing to a minimal realization of Bose-Einstein condensation of photons.

Divacancies, atom-sized defects, are potential building blocks for future quantum networks, but controlling and communicating with them requires demanding capabilities. New experiments show that divacancies in a form of silicon carbide can be isolated and allow for coherent transfer of quantum information between their spin and light.

Life thrives under an enormous range of temperature and pressures, but it’s not clear how proteins are naturally selected to match their environment. New computer simulations demonstrate the critical role that water plays in this selection as well as stability differences between proteins selected at low and high temperatures.

Optical isolators, which are critical for preventing feedback in optical devices, are difficult to miniaturize because of the need to use centimeter-sized crystals. New experiments show a potential way around this hurdle by using embedded nanoscale wires to enhance Faraday rotation in a thin film.

Cell populations that are starved for nutrients can enter a little-understood stationary phase where growth is stopped without the cells dying off. A new model of a cell exhibits the same behavior that is seen in experiments, providing insight into how cells respond to nutrient depletion.

Quantum computers will need to be tolerant to errors introduced by noise, but current proposals estimate that the number of qubits required for error correction will be many orders of magnitude larger than the number needed for useful computation. A new proposal uses a classical-quantum hybrid scheme to implement simple error-tolerant quantum processors with relatively few resources.

Stochastic thermodynamics extends the traditional laws of thermodynamics to microscopic systems where thermal and quantum fluctuations cannot be ignored. This review summarizes progress in this field with a look at several experimental and theoretical results and a look toward potential applications in biology and nanotechnology.