Review Articles in 2020

Strong correlations may produce states of matter that do not have non-interacting counterparts, with new types of quantum criticality, superconductivity, and topological phases being recent highlights. This Review describes the physics underlying these correlated states and points to their potential for quantum applications.

Since the first measurement of the spin structure of the proton, there has been significant theoretical and experimental progress in understanding the origins of the proton spin. This Review discusses what we have learned so far, what is still missing and what to expect from the upcoming experiments.

A variety of quantum programming languages have been developed over the past few years, enabling newcomers and seasoned practitioners alike. This Review gives a brief introduction to quantum programming, overviewing some of the existing languages and the ecosystem around them.

The rapidly developing field of topological data analysis represents data via graphs rather than as solutions to equations or as decompositions into clusters. This Review discusses the methods and provides examples from physics and other sciences.

The past decade has witnessed remarkable progress in our understanding of equilibration, thermalization and prethermalization, due in large part to experimental breakthroughs in ultracold atomic gases. This Review discusses theoretical and experimental advances on these topics and the challenges ahead.

Axion fields provide a unique way to understand large quantized electromagnetic responses in topological insulators and dynamics in Weyl semimetals. This Review discusses the theory of axion fields in condensed matter, their experimental realization and their application in next-generation devices.

The charge radius of the proton is controversial because measurements by different methods disagree. Recent results indicate that these measurements might be reconciled. In this Review, we discuss the experimental techniques used to measure the proton radius and describe the current status of the field as well as forthcoming experiments.

Holographic duality is an equivalence relation between a gravitational system and a quantum many-body system. The Review discusses various insights obtained from the duality into properties of strongly coupled matter, quantum many-body chaos and deep connections between quantum information and geometry.

The coupling of photons to material quasiparticles such as plasmons, phonons and excitons opens new possibilities in light–matter interactions. This Review presents a generalized view of such quasiparticles and the technique that describes their interactions with matter: macroscopic quantum electrodynamics.

Topological Majorana bound states have potential for encoding, manipulating and protecting quantum information in condensed-matter systems. This Review discusses emergence and characterization of Majorana bound states in realistic devices based on hybrid semiconducting nanowires and their connection to more conventional Andreev bound states.

Ferroelectric and ferroelastic domain walls are 2D topological defects with thicknesses approaching the unit cell level and emergent functional properties. This Review discusses the exotic polarization profiles that arise at domain walls and the fundamental mechanisms responsible for domain-wall conduction.

2D materials host various collective excitations, which either mutate or cease to exist in the bulk. In this Review, we select the most striking properties of 2D plasmons, excitons, phonons and magnons, contrasting them with the bulk versions.

Understanding the behaviour of materials at high pressures and temperatures is of great importance to planetary science and the physics of warm dense matter. This Review addresses the close connection between modelling the interiors of gaseous planets and the high-pressure physics of hydrogen and helium.

The Kondo insulator samarium hexaboride is the first experimentally demonstrated example of a strongly correlated topological insulator. This article reviews the topological theory and experimental evidence, including a mystery as to the origin of quantum oscillations and their relation to possible unconventional bulk in-gap states.

Despite comprising only about 15% of the known molecular inventory of the interstellar medium, molecular ions have an outsized role in driving chemical evolution. This Review examines the advances — and challenges — in laboratory spectroscopy that have enabled the study of ions in space.

The study of higher-dimensional quantum states has seen numerous conceptual and technological developments. This review discusses various techniques for the generation and processing of qudits, which are stored in the momentum, path, time-/frequency-bins, or the orbital angular momentum of photons.

Chemical vapour deposition (CVD) enables the synthesis of high-purity, pinhole-free and conformal polymer thin films. This Review discusses the recent breakthroughs in mechanistically based CVD polymerization processes and designing CVD polymers for a diverse array of applications.

Time-periodic fields provide a versatile platform for inducing non-equilibrium topological phenomena in quantum systems. We discuss how such fields can be used for topological band structure engineering, and the conditions for observing robust topological behaviour in a many-body setting.

Optical microscopy is limited to shallow in vivo imaging depths owing to the exponential extinction of single-scattered waves by multiple light scattering. In this Review, we survey methodologies for deep optical imaging that maintain microscopic resolution by making deterministic use of multiple-scattered waves.

The integration of gate-defined quantum dots with superconducting resonators results in a hybrid architecture that holds promise for quantum information processing. This Review discusses recent experimental results in the field, including the achievement of strong coupling between single microwave photons and the charge and spin degrees of freedom, and examines the underlying physics.