Volume 18 Issue 8, August 2022

Across the world, decisions on investment and policy are made under the assumption of continuous economic expansion. Fundamental physical limits may soon put an end to this phase of development, as foreshadowed by the 1972 report The Limits to Growth.

A fundamental technical challenge in the analysis of network data is the automated discovery of communities — groups of nodes that are strongly connected or that share similar features or roles. In this Comment we review progress in the field over the past 20 years.

Experiments with chiral magnets may hold the key to a better understanding of fundamental aspects of transformations between different skyrmionic states, necessary for magnetic memory and logic applications to become a reality.

Quantum confinement effects offer a more comprehensive understanding of the fundamental processes that drive extreme optical nonlinearities in nano-engineered solids, opening a route to unlocking the potential of high-order harmonic generation.

Originally suggested for the detection of gravitational waves, resonantly vibrating metal beams have been used in a recent laboratory experiment to measure Newton’s constant of gravitation and to verify Newton’s gravitational law.

The hydrodynamic description of many-body quantum systems is a key part of our understanding of out-of-equilibrium physics. Exotic, highly constrained quantum particles called fractons require a treatment that goes beyond hydrodynamics.

Colloidal random lasers are hard to design and control. Combining optically controlled micro-heaters with thermophilic particles attracted by them leads to microlasers with programmable and reversible patterns.

Magnetic skyrmions—a type of localized spin texture—have been theoretically predicted to annihilate with counterparts known as antiskyrmions. By means of electron microscopy, such annihilation has now been observed in a cubic chiral magnet.

Unconventional superconductivity is often associated with the presence of other kinds of electronic order. Observations of charge order in infinite-layer nickelate superconductors show that they fit this pattern.

Both inter- and intraband transitions contribute to high-harmonic generation in solids, but their exact roles are not fully understood. Experiments with quantum dots show that enhanced intraband transitions lead to increased carrier injection and thus enhanced harmonic generation.

A method to engineer higher-order interactions between photons provides a route to create non-classical and entangled states across multiple modes.

Topological states characterized by Chern numbers are usually considered to be the global properties of a material. Now a spatial patchwork of different Chern insulator states is imaged in twisted bilayer graphene.

Continuously changing the coupling between a magnetic impurity and a superconductor allows the observation of the reversal of supercurrent flow at the atomic scale.

In generic quantum many-body systems, initial configurations far from equilibrium are expected to undergo general thermalization. An experiment with ultracold atoms now shows evidence of a class of spin-helix states that evade such behaviour.

Thermal fluctuations associated with higher temperatures normally destroy long-range order, but in some circumstances they can stabilize new ordered phases. This ‘order by disorder’ phenomenon has now been observed in the magnetic phases of neodymium.

Fractons are particles that can only move in tandem, which substantially affects their thermalization. Below four spatial dimensions, an unconventional dynamical universality class can emerge as thermal fluctuations destroy hydrodynamic behaviour.

Interactive protocols can verify that a quantum computer exhibits a computational speedup using only classical analysis of its output. Exploiting a connection to Bell’s theorem gives a simpler protocol that is much less demanding for experiments.

The standard quantum limit bounds the precision of quantum measurements. Now, a protocol based on time-reversal operations with cold atoms overcomes that limit and achieves the greatest phase sensitivity improvement in any full Ramsey interferometer.

Uncovering structures in temporal networks requires different tools than in their static counterparts. A metric now quantifies whether the nodes with a large number of connections also tend to stay simultaneously connected for longer times.

Experiments inspired by the behaviour of active matter show that an external optical stimulus can spatially reconfigure colloidal random lasers and continuously tune their lasing threshold.

The first step of biofilm formation is a transition from a single layer of bacteria to multiple layers. Now, there is evidence that this transition is determined by the phenotypic noise associated with cell geometry and growth rate.

Measurements of the gravitational interaction between two parallel beams vibrating in bending motion enable the quantitative investigation of dynamic gravitation in the hertz regime and allow the determination of the gravitational constant.

The digital transformation doesn’t stop at metrology as Shanay Rab, Meher Wan and Sanjay Yadav explain.