Volume 18 Issue 1, January 2022

Magnons are collective spin excitations that can propagate over long distances — an attractive trait for information-transfer technologies — but we need to better understand their thermodynamic properties. A platform using graphene may hold the key.

Nonlinear optical effects are by default weak but they can be enhanced by sculpting the resulting spectrally periodic pulses from a fibre laser into an optimal shape.

A condensate of excitons was theoretically conjectured in the 1960s but has been challenging to pinpoint experimentally. Evidence has now emerged that it could be the ground state of tungsten ditelluride, a rich topological material.

The reliability of quantum computers depends on the correction of noise-induced errors, which requires additional resources. Experiments on superconducting qubits have now demonstrated the capabilities of a less-demanding scheme for error detection.

Promising machine learning techniques can deduce the properties of merging black holes from gravitational wave signals a million times faster than current state-of-the-art methods.

Solid-state sources of entangled photons with tailored properties are key elements for integrated quantum computing. Refractive-index perturbations propagating faster than the speed of light may offer a practical approach for generating entangled photon pairs.

Interaction with light can be used to precisely control motional states. This Review surveys recent progress in the preparation of non-classical mechanical states and in the application of optomechanical platforms to specific tasks in quantum technology.

Accurate measurements of the ohm require high magnetic fields to support the quantum Hall effect. Now, high precision is achieved by using the quantum anomalous Hall effect in a low magnetic field, making the measurement much more accessible.

Stacking and twisting two-dimensional materials has led to the observation of a variety of electronic phenomena. Now, magnetic behaviour that is distinct from anything seen in individual layers is induced by a moiré pattern in double bilayer chromium triiodide.

Although magnons in the quantum Hall regime of graphene have been detected, their thermodynamic properties have not yet been measured. Now, a local probe technique enables the detection of the magnon density and chemical potential.

Topological states that are created from strong electron–electron interactions at half-integer superlattice fillings are observed at zero magnetic field.

Twisted double bilayer graphene is predicted to be a topological insulator under certain conditions. Simultaneous bulk and edge measurements now show metallic transport with a bulk bandgap, suggestive of this prediction.

The LHCb collaboration reports an improved measurement of the oscillation frequency of mesons consisting of a bottom quark and strange quark, which is then combined with previous results.

The nonlinear optical effects underlying many applications are typically weak, but linear dispersion engineering allows the generation of pulses comprising equidistant frequency components, which enhances the effective nonlinearity.

Despite their relevance for quantum technology, photon-pair sources are difficult to control. A theoretical proposal shows how photon pairs can be created from vacuum fluctuations in time-dependent systems, potentially enabling heralded single-photon frequency combs.

Evaluations of quantum computers across architectures need reliable benchmarks. A class of benchmarks that can directly reflect the structure of any algorithm shows that different quantum computers have considerable variations in performance.

Large-scale quantum computers will manipulate quantum information encoded in error-corrected logical qubits. A complete set of operations has now been realized on a logical qubit with error detection.

Insulating states that are formed because of pairing between electrons and holes are known to exist in engineered bilayer structures in high magnetic fields. Now evidence suggests they can occur in a monolayer crystal at zero field.

Exciton condensation has been observed in various three-dimensional (3D) materials. Now, monolayer WTe₂—a 2D topological insulator—also shows the phenomenon. Strong electronic interactions allow the excitons to form and condense at high temperature.

Network models rarely fix the number of connections of each node during evolution, despite this being needed in real-world applications. Addressing this need, a new approach can grow scale-free networks without preferential attachment.

Cosmic rays flying through superconducting quantum devices create bursts of excitations that destroy qubit coherence. Rapid, spatially resolved measurements of qubit error rates make it possible to observe the evolution of the bursts across a chip.

A method for estimating the source properties of gravitational-wave events shows a speed-up of six orders of magnitude over established approaches. This is a promising tool for follow-up observations of electromagnetic counterparts.

To celebrate the International Year of Basic Sciences for Sustainable Development, James Gallagher tells the story of the British thermal unit, a unit for heat.