Articles in 2021

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.

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.

The modern understanding of quantum transport relies on geometric concepts such as the Berry phase. The geometric approach has now been extended to the theory of optical transitions.

The complexity of many-body quantum states makes their evolution difficult to simulate with classical computers. Experiments on a 2D nine-qubit device demonstrate that the key properties of quantum lattices can be accessed by measuring out-of-time-ordered correlators.

Observations of an electronic nematic phase in twisted double bilayer graphene expand the number of moiré materials where this interaction-driven state exists.

A general theoretical technique is introduced to identify materials that host flat bands. Applying topological quantum chemistry provides the generating bases for these flat bands in all space groups.

Cuprates exhibit exotic states because of the interplay between spin, charge and orbital degrees of freedom. Ab initio calculations now show that a mechanism called orbital expansion plays a key role in the magnetic properties of cuprates.

Nonlinear interferometry based on time reversal enables entanglement-enhanced measurements without the need for low-noise detection. An alternative approach now exploits cyclic dynamics and shows performance beyond the standard quantum limit.

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.

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.

Although it shows promise for applications, non-Abelian braiding is difficult to realize in electronic systems. Its demonstration using acoustic waveguides may provide a useful platform to study non-Abelian physics.

Comparing ways of arranging catalysts in living systems reveals that the reaction- and diffusion-limited regimes require different strategies. The formalism generalizes the Thomson problem of optimizing the configuration of electrons on a sphere.

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.

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.

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.

The addition of transverse forces to an ensemble of colloidal spinners induces the appearance of odd elastic crystals, featuring self-propelled defects that organize the system into a ‘self-kneading’ crystal whorl state.

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 search for transient dark matter in the form of domain walls of axion-like particles finds no statistically significant signal. This places constraints on our theoretical understanding of such scenarios.

Information theory sets an upper limit on the ability of bacteria to navigate up chemical gradients. Experiments reveal that cells do so at speeds within a factor of two of the limit, suggesting they are selected to efficiently use information.