Single-molecule technology stands as a powerful tool, enabling the characterization of intricate structural and dynamic information that would otherwise remain concealed within the averaged behaviors of numerous molecules. This technology finds extensive application across diverse fields including physics, chemistry, biology, and medicine. Quantum sensing, particularly leveraging nitrogen-vacancy (NV) centers within diamond structures, presents a promising avenue for single-molecule magnetic resonance, offering prospects for sensing and imaging technology at the single-molecule level. Notably, while significant strides have been made in single-molecule scale magnetic resonance using NV centers over the past two decades, current approaches still exhibit limitations in magnetic sensitivity, spectral resolution, and spatial resolution. In particular, the full reconstruction of three-dimensional positions of nuclear spins within single molecules remains an unattained goal. This review provides a comprehensive overview of the current state of the art in single-molecule scale magnetic resonance encompassing an analysis of various relevant techniques involving NV centers. Additionally, it explores the optimization of technical parameters associated with these methods. This detailed analysis serves as a foundation for the development of new technologies and the exploration of potential applications.

Mechanical vibrations are being harnessed for a variety of purposes and at many length scales, from the macroscopic world down to the nanoscale. The considerable design freedom in mechanical structures allows one to engineer new functionalities. In recent years, this has been exploited to generate setups that offer topologically protected transport of vibrational waves (topological phonon transport), both in the solid state and in fluids. Borrowing concepts from electronic physics and being cross fertilized by concurrent studies for cold atoms and electromagnetic waves, this field of topological transport in engineered mechanical systems offers a rich variety of phenomena and platforms. In this Colloquium, a unifying overview of the various ideas employed in this area is provided, different approaches and experimental implementations are summarized, and the challenges as well as the prospects are commented upon.

Magnetotactic bacteria are swimming microorganisms able to follow magnetic field lines with the help of an organelle called the magnetosome that is made of biomineralized magnetic crystals assembled in a chain. In combination with this ability, these bacteria perform active oxygen sensing to reach the oxic-anoxic transition zone, which is often located in the upper part of the sediment. From a physicist’s perspective, magnetotactic bacteria can be seen at the interface between bacterial active matter and magnetic colloids, which gives them unique properties at both the individual and collective levels. In crowded media and/or when they are submitted to external flows, their motion can be efficiently driven by magnetic fields, which leads to surprising effects. In this Colloquium, the different features of magnetotactic bacteria at are reviewed at every scale, from single cell to collective motion, from simple to complex environments, and by emphasizing the differences from other bacterial species or passive magnetic colloids. The Colloquium concludes with a discussion of perspectives on using magnetotactic bacteria in active magnetorheology.

The striking success of the standard model in explaining precision data and, at the same time, its lack of explanations for various fundamental phenomena, such as dark matter and the baryon asymmetry of the Universe, suggest new physics at an energy scale that greatly exceeds the electroweak scale. In the absence of a short-range–long-range conspiracy, the standard model can be viewed as the leading term of an effective “remnant” theory (referred to as the SMEFT) of a more fundamental structure. In recent years, many aspects of the SMEFT have been investigated, and it has become a standard tool for analyzing experimental results in an integral way. In this review, after a presentation of the salient features of the standard model, the construction of the SMEFT is reviewed. The range of its applicability and bounds on its coefficients imposed by general theoretical considerations are discussed. Since new-physics models are likely to exhibit exact or approximate accidental global symmetries, especially in the flavor sector, their implications for the SMEFT are also discussed. The main focus of the review is the phenomenological analysis of experimental results. How to use various effective field theories to study the phenomenology of theories beyond the standard model is explicitly shown. Descriptions of the matching procedure and the use of the renormalization group equations are given, allowing one to connect multiple effective theories that are valid at different energy scales. Explicit examples from low-energy experiments and from high-$p_T$ physics illustrate the workflow. Also commented upon are the nonlinear realization of electroweak symmetry breaking and its phenomenological implications.

The remanent magnetization of ferromagnets has long been studied and used to store binary information. While early magnetic memory designs relied on magnetization switching by locally generated magnetic fields, key insights in condensed matter physics later suggested the possibility of doing it by electrical means instead. In the 1990s, Slonczewski and Berger formulated the concept of current-induced spin torques in magnetic multilayers through which a spin-polarized current generated by a first ferromagnet may be used to switch the magnetization of a second one. This discovery drove the development of spin-transfer-torque magnetic random-access memories (MRAMs). More recent fundamental research revealed other types of current-induced torques named spin-orbit torques (SOTs) and will lead to a new generation of devices including SOT MRAMs and skyrmion-based devices. Parallel to these advances, multiferroics and their magnetoelectric coupling, first investigated experimentally in the 1960s, experienced a renaissance. Dozens of multiferroic compounds with new magnetoelectric coupling mechanisms were discovered and high-quality multiferroic films were synthesized (notably of ${\mathrm{BiFeO}}_3$), also leading to novel device concepts for information and communication technology such as the magnetoelectric spin-orbit (MESO) transistor. The story of the electrical switching of magnetization, which is discussed in this review, is that of a dance between fundamental research (in spintronics, condensed matter physics, and materials science) and technology (MRAMs, MESO transistors, microwave emitters, spin diodes, skyrmion-based devices, components for neuromorphics, etc.). This pas de deux has led to major scientific and technological breakthroughs in recent decades (such as the conceptualization of pure spin currents, the observation of magnetic skyrmions, and the discovery of spin-charge interconversion effects). As a result, this field has not only propelled MRAMs into consumer electronics products but also fueled discoveries in adjacent research areas such as ferroelectrics or magnonics. In this review, recent advances in the control of magnetism by electric fields and by current-induced torques are covered. Fundamental concepts in these two directions are reviewed first, their combination is then discussed, and finally current various families of devices harnessing the electrical control of magnetic properties for various application fields are addressed. The review concludes by giving perspectives in terms of both emerging fundamental physics concepts and new directions in materials science.

Scalarization is a mechanism that endows strongly self-gravitating bodies, such as neutron stars and black holes, with a scalar-field configuration. It resembles a phase transition in that the scalar configuration appears only when a certain quantity that characterizes the compact object, for example, its compactness or spin, is beyond a threshold. A critical and comprehensive review of scalarization, including the mechanism itself, theories that exhibit it, its manifestation in neutron stars, black holes and their binaries, potential extension to other fields, and a thorough discussion of future perspectives, is provided.

Angle-resolved photoemission spectroscopy (ARPES), with its exceptional sensitivity to both the binding energy and the momentum of valence electrons in solids, provides unparalleled insight into the electronic structure of quantum materials. Over the past two decades, the advent of femtosecond lasers, which can deliver ultrashort and coherent light pulses, has ushered the ARPES technique into the time domain. Currently time-resolved ARPES (TR-ARPES) can probe ultrafast electron dynamics and the out-of-equilibrium electronic structure, providing a wealth of information that is otherwise unattainable in conventional ARPES experiments. This review begins with an introduction to the theoretical underpinnings of TR-ARPES followed by a description of recent advances in state-of-the-art ultrafast sources and optical excitation schemes. It then reviews paradigmatic phenomena investigated by TR-ARPES thus far, such as out-of-equilibrium electronic states and their spin dynamics, Floquet-Volkov states, photoinduced phase transitions, electron-phonon coupling, and surface photovoltage effects. Each section highlights TR-ARPES data from diverse classes of quantum materials, including semiconductors, charge-ordered systems, topological materials, excitonic insulators, Van der Waals materials, and unconventional superconductors. These examples demonstrate how TR-ARPES has played a critical role in unraveling the complex dynamical properties of quantum materials. The conclusion outlines possible future directions and opportunities.

Diffusion driven by temperature or concentration gradients is a fundamental mechanism of energy and mass transport that inherently differs from wave propagation in both physical foundations and application prospects. Compared with conventional schemes, metamaterials provide an unprecedented potential for governing diffusion processes, based on emerging theories like the transformation and the scattering-cancellation theory that expanded the original concepts and suggested innovative metamaterial-based devices. The term diffusionics is used in the review to generalize these noteworthy achievements in various energy and mass diffusion systems. Examples include heat diffusion systems and particle and plasma diffusion systems. For clarity the numerous studies published over the past decade are categorized by diffusion field (i.e., heat, particles, and plasmas) and discussed from three different perspectives: the theoretical perspective, to detail how the transformation principle is applied to each diffusion field; the application perspective, to introduce various interesting metamaterial-based devices, such as cloaks and radiative coolers; and the physics perspective, to connect them with concepts of recent concern, such as non-Hermitian topology, nonreciprocal transport, and spatiotemporal modulation. The possibility of controlling diffusion processes beyond metamaterials is also discussed. Finally, several future directions for diffusion metamaterial research, including the integration of metamaterials with artificial intelligence and topology concepts, are examined.

A plethora of two-dimensional (2D) materials have been introduced in physics and engineering in the past two decades. Their robust, membranelike sheets permit (mostly require) deposition, giving rise to solid-solid dry interfaces whose mobility, pinning, and general tribological properties under shear stress are currently being understood and controlled, both experimentally and theoretically. In this Colloquium simulated case studies of twisted graphene systems are used as a prototype workhorse tool to demonstrate and discuss the general picture of 2D material interface sliding. First highlighted is the crucial mechanical difference, often overlooked, between small and large incommensurabilities, which corresponds to, for example, small and large twist angles in graphene interfaces. In both cases, focusing on flat, structurally lubric or “superlubric” geometries, the generally separate scalings with the area of static friction in pinned states and of kinetic friction during sliding are elucidated and reviewed, tangled as they are with the effects of velocity, temperature, load, and defects. The roles of island boundaries and elasticity are also discussed, and compared when possible to results in the literature for systems other than graphene. It is proposed that the resulting picture of pinning and sliding should be applicable to interfaces in generic 2D materials that are of importance for the physics and technology of existing and future bilayer and multilayer systems.

A comprehensive theory of the Lamb shift in light muonic atoms such as $\mu \mathrm{H}$, $\mu \mathrm{D}$, ${\mu }^3{\mathrm{He}}^{+}$, and ${\mu }^4{\mathrm{He}}^{+}$ is presented, with all quantum electrodynamic corrections included at the precision level constrained by the uncertainty of nuclear structure effects. This analysis can be used in the global adjustment of fundamental constants and in the determination of nuclear charge radii. Further improvements in the understanding of electromagnetic interactions of light nuclei will allow for a promising test of fundamental interactions by comparison with “normal” atomic spectroscopy, in particular, with H-D and ${}^3\mathrm{He}\text{−}{}^4\mathrm{He}$ isotope shifts.

The burgeoning field of “fractons,” a class of models where quasiparticles are strictly immobile or display restricted mobility that can be understood through generalized multipolar symmetries and associated conservation laws, is reviewed. With a focus on merely a corner of this fast-growing subject, it is demonstrated how one class of such theories, symmetric tensor and coupled-vector gauge theories, surprisingly emerge from familiar elasticity of a two-dimensional quantum crystal. The disclination and dislocation crystal defects, respectively, map onto charges and dipoles of the fracton gauge theory. This fracton-elasticity duality leads to predictions of fractonic phases and quantum phase transitions to their descendants that are duals of the commensurate crystal, supersolid, smectic, and hexatic liquid crystals, as well as amorphous solids, quasicrystals, and elastic membranes. It is shown how these dual gauge theories provide a field-theoretic description of quantum melting transitions through a generalized Higgs mechanism. It is demonstrated how they can be equivalently constructed as gauged models with global multipole symmetries. Extensions of such gauge-elasticity dualities to generalized elasticity theories are expected to provide a route to the discovery of new fractonic models and their potential experimental realizations.

Proton imaging has become a key diagnostic for measuring electromagnetic fields in high-energy-density (HED) laboratory plasmas. Compared to other techniques for diagnosing fields, proton imaging is a measurement that can simultaneously offer high spatial and temporal resolution and the ability to distinguish between electric and magnetic fields without the protons perturbing the plasma of interest. Consequently, proton imaging has been used in a wide range of HED experiments, from inertial-confinement fusion to laboratory astrophysics. An overview is provided on the state of the art of proton imaging, including a discussion of experimental considerations like proton sources and detectors, the theory of proton-imaging analysis, and a survey of experimental results demonstrating the breadth of applications. Topics at the frontiers of proton-imaging development are also described, along with an outlook on the future of the field.

The physics of the gravitational form factors of the proton, as well as their understanding within quantum chromodynamics, has advanced significantly in the past two decades through both theory and experiment. This Colloquium provides an overview of this progress, highlights the physical insights unveiled by studies of gravitational form factors, and reviews their interpretation in terms of the mechanical properties of the proton.

A quantum internet is the holy grail of quantum information processing, enabling the deployment of a broad range of quantum technologies and protocols on a global scale. However, numerous challenges must be addressed before the quantum internet can become a reality. Perhaps the most crucial of these is the realization of a quantum repeater, an essential component in the long-distance transmission of quantum information. As the analog of a classical repeater, extender, or booster, the quantum repeater works to overcome loss and noise in the quantum channels constituting a quantum network. Here the conceptual frameworks and architectures for quantum repeaters, as well as the experimental progress toward their realization, are reviewed. Various near-term proposals to overcome the limits to the communication rates set by point-to-point quantum communication are also discussed. Finally, the manner in which quantum repeaters fit within the broader challenge of designing and implementing a quantum internet is overviewed.

For quantum computers to successfully solve real-world problems, it is necessary to tackle the challenge of noise: the errors that occur in elementary physical components due to unwanted or imperfect interactions. The theory of quantum fault tolerance can provide an answer in the long term, but in the coming era of noisy intermediate-scale quantum machines one must seek to mitigate errors rather than completely eliminate them. This review surveys the diverse methods that have been proposed for quantum error mitigation, assesses their in-principle efficacy, and describes the hardware demonstrations achieved to date. Commonalities and limitations among the methods are identified, while mention is made of how mitigation methods can be chosen according to the primary type of noise present, including algorithmic errors. Open problems in the field are identified, and the prospects for realizing mitigation-based devices that can deliver a quantum advantage with an impact on science and business are discussed.

Kinematic variables play an important role in collider phenomenology, as they expedite discoveries of new particles by separating signal events from unwanted background events and allow for measurements of particle properties such as masses, couplings, and spins. For the past ten years, an enormous number of kinematic variables have been designed and proposed, primarily for the experiments at the CERN Large Hadron Collider, allowing for a drastic reduction of high-dimensional experimental data to lower-dimensional observables, from which one can readily extract underlying features of phase space and develop better-optimized data-analysis strategies. Recent developments in the area of phase-space kinematics are reviewd, and new kinematic variables with important phenomenological implications and physics applications are summarized. Recently proposed analysis methods and techniques specifically designed to leverage new kinematic variables are also reviewed. As machine learning is currently percolating through many fields of particle physics, including collider phenomenology, the interconnection and mutual complementarity of kinematic variables and machine-learning techniques are discussed. Finally, the manner in which utilization of kinematic variables originally developed for colliders can be extended to other high-energy physics experiments, including neutrino experiments, is discussed.

The optics of correlated disordered media is a conceptually rich research topic emerging at the interface between the physics of waves in complex media and nanophotonics. Inspired by photonic structures in nature and enabled by advances in nanofabrication processes, recent investigations have unveiled how the design of structural correlations down to the subwavelength scale could be exploited to control the scattering, transport, and localization of light in matter. From optical transparency to superdiffusive light transport to photonic gaps, the optics of correlated disordered media challenges our physical intuition and offers new perspectives for applications. This review examines the theoretical foundations, state-of-the-art experimental techniques, and major achievements in the study of light interaction with correlated disorder, covering a wide range of systems: from short-range correlated photonic liquids to Lévy glasses containing fractal heterogeneities to hyperuniform disordered photonic materials. The mechanisms underlying light scattering and transport phenomena are elucidated on the basis of rigorous theoretical arguments. Ongoing research on mesoscopic phenomena such as transport phase transitions and speckle statistics and the current development of disorder engineering for applications such as light-energy management and visual appearance design are overviewed. Finally, special efforts are made to identify the main theoretical and experimental challenges to address in the near future.

New particle formation of liquid or solid nanoparticles from gas-phase precursors is a decisive process in Earth’s atmosphere and is considered one of the largest uncertainties in climate change predictions. Key for the climate relevance of new particle formation is the growth of freshly formed molecular clusters, as it determines the survival of these particles to cloud condensation nuclei sizes, where they can contribute to the aerosol-indirect effect. This review lays out the fundamental definitions of nanoparticle growth and addresses the rapidly emerging field of new particle formation studies with a focus on the diverse processes contributing to nanoparticle growth, explicitly comparing the latest experimental findings and their implementation in large-scale models. Atmospheric nanoparticle growth is a complex phenomenon including condensational and reactive vapor uptake, aerosol coagulation, and sink processes. It is linked to thermodynamics, cluster- and phase-transition physics. Nanoparticle growth rates measured from the evolution of the particle-size distribution describe growth as a collective phenomenon, while models often interpret them on a single-particle level and incorporate it into highly simplified size-distribution representations. Recent atmospheric observations show that sulfuric acid together with ammonia and amines, iodic acid, and oxidized organic species can contribute to nanoparticle growth, whereas most models describe the growth effects from a limited subset of this variety of condensable vapors. Atmospheric simulation chamber experiments have clarified the role of ions, intermolecular forces, the interplay of acids and bases, and the contribution of different types of organic vapors. Especially in the complex thermodynamics of organic vapor condensation, the field has had noteworthy advances over the last decade. While the experimental field has achieved significant progress in methodology and process level understanding, this has not led to a similar improvement in the description of the climate impact of nanoparticle formation in large-scale models. This review sets the basis to better align experimental and modeling studies on nanoparticle growth, giving specific guidance for future studies aiming to resolve the questions as to why the climate response in large-scale models seems to be buffered against high survival probabilities and why the global growth observations herein show surprisingly low variation.