Articles in 2021

The dynamics of quantum information and entanglement is closely linked to the physics of thermalization. A quantum simulator comprised of superconducting qubits has measured the spread of quantum information in a many-body system.

Observations of an electronic state where rotational symmetry is broken show that this could be a generic feature of moiré materials.

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.

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.

Active matter exhibits a plethora of collective phenomena in both biological and artificial systems. In a model system of colloidal rollers, polar states in active liquids can be controlled.

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.

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.

Superconducting devices ubiquitously have an excess of broken Cooper pairs, which can hamper their performance. It is widely believed that external radiation is responsible but a study now suggests there must be an additional, unknown source.

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.

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.

The performance of superconducting devices can be degraded by quasiparticle generation mechanisms that are difficult to identify and eliminate. Now, a small superconducting island can be kept quasiparticle free for seconds at a time.

Acoustic waveguides have been used to implement the long-theorized phenomenon of non-Abelian braiding, in which abstract geometric constructions are used to generate transformations between different modes.