Reviews & Analysis

Fifty years after the publication of Philip Anderson’s landmark essay ‘More is different’ that crystallized the idea of emergence, eight scientists describe the most interesting phenomena that emerge in their fields.

Understanding the fundamental limits to photonic design is both theoretically important and critical to the development of future high-performance photonic devices. This Review surveys progress made in this area and discusses an emerging general framework for evaluating photonic design limits based on conservation principles and optimization theory.

The study of Bose–Einstein condensation in photonic systems has attracted strong interest in a variety of physical platforms, including conventional lasers and optical parametric oscillators, exciton and exciton–polariton gases, and photons in dye-filled cavities and propagating geometries. The focus of this Review is to highlight those universal phenomena that stem from the driven-dissipative, non-equilibrium nature of these systems and affect the static, dynamic, superfluid and coherence properties of the condensate.

Flat bands enhance the effect of electronic interactions and have emerged as a promising platform for superconductivity. This Review explains the quantum geometric origin of flat-band superconductivity and superfluidity, and discusses its relevance in graphene and ultracold gas moiré systems.

Owing to the growing volumes of data from high-energy physics experiments, modern deep learning methods are playing an increasingly important role in all aspects of data taking and analysis. This Review provides an overview of key developments, with a focus on the search for physics beyond the standard model.

The polarization of the cosmic microwave background (CMB) may shed light on the nature of dark matter and dark energy, and on the origin of all structures in the Universe. Discovering a signature of such new physics in the CMB will require new observational and calibration strategies for future CMB experiments.

Living cells use geometric, biochemical and mechanical guiding cues to control intracellular protein patterns that regulate many vital functions. This Review discusses mechanisms of pattern guidance unveiled in living cells and how to study them from a physics perspective.

The standard Hamiltonian approach to quantum field theory violates Poincaré invariance, leading to predictions with artificial dynamical effects and potentially obscuring the fundamental description of a physical system. This Perspective explains how such issues are avoided by using light-front Hamiltonian quantization.

Active matter encompasses various non-equilibrium systems in which individual constituents convert energy into non-conservative forces or motion at the microscale. This Review provides an elementary introduction to the role of topology in active matter through experimentally relevant examples.

Minimizing the energy of the Ising model is a prototypical combinatorial optimization problem, ubiquitous in our increasingly automated world. This Review surveys Ising machines — special-purpose hardware solvers for this problem — and examines the various operating principles and compares their performance.

Polaritonics is the physics of strongly coupled light–matter states that studies condensates and superfluids of bosonic quasiparticles in solid-state systems. Coherent flows of exciton–polaritons can be used for classical and quantum information processing, offering advantages of full optical control and read-out.

Electric-double-layer transistors and ionic field-effect transistors enable continuous tuning of carrier densities in 2D superconductors, which are essential for studying novel quantum phenomena and finding new high-temperature superconductors. This Review summarizes recent advances and future development paths for electric-field-gated superconductivity in various ultrathin superconducting materials, including iron-based superconductors, transition-metal dichalcogenides, honeycomb bilayer superconductors and cuprates.

Finding the most appropriate machine learning algorithm for the analysis of any given scientific dataset is currently challenging, but new machine learning benchmarks for science are being developed to help.

Multi-messenger observations of gravitational waves and electromagnetic radiation directly probe the synthesis of heavy elements in the Universe. This Review summarizes recent results and charts future challenges and opportunities for identifying the astrophysical origin of roughly half of the elements heavier than iron.

New approaches to integrate high-dimensional recordings of brain activity with single-neuron resolution with simultaneous recordings of natural animal behaviour enable the study of brain-wide activity in small animals including worms, flies and fish during behaviours and decision-making. This Review surveys experimental and theoretical approaches that have opened this area of systems neuroscience.

Mastering thermal conductivities of materials under pressure is extremely important for managing thermal processes, understanding the thermal transport mechanisms and for potential technological applications. This Review surveys the progresses in technique developments, research results and scientific implications in this field.

Graphene oxide (GO) has attracted intensive research interest, owing to remarkable physicochemical properties. Nevertheless, its high chemical reactivity and low stability may lead to uncontrolled GO derivatives. The chemistry of GO can be controlled by selective derivatization of the oxygenated groups and C=C bonds and by appropriate characterization.

The observation of gravitational waves emitted in the merger of neutron stars and the observations of X-rays emitted by hotspots on their surfaces are beginning to reveal nuclear physics insights about these compact objects.

Magnetic reconnection explosively releases stored magnetic energy in astrophysical plasmas. Thanks to advances in observations, exascale computing and multiscale experiments, it will be possible to solve outstanding physics problems, including the immense separation between global and dissipation scales, reconnection onset and particle acceleration.

Much of the rich phenomenology of active matter can be traced back to violations of time-reversal symmetry and departure from Boltzmann statistics. This Review disentangles these nonequilibrium signatures for interacting and dilute systems, in the presence of obstacles and external potentials.