Volume 19 Issue 7, July 2023

Although quantum spin liquids have long been theoretically studied, an experimental demonstration has remained challenging. An inorganic oxide presents an ideal candidate to realize this disordered state.

The combination of magnetic and non-magnetic layers in (MnBi₂Te₄)(Bi₂Te₃) is predicted to produce topologically protected states on the surface. Experiments now show that the nature of the topmost layer controls the location of these states.

The structure of disordered materials typically ages, but sometimes also rejuvenates, resulting in intriguing memory properties. Progress in numerical simulations of spin glasses has now enabled replication of such phenomena from simple models.

Time-varying photonics constitutes an emerging concept where a material’s time-dependence is used to achieve novel functionalities. A temporal double-slit-diffraction experiment demonstrates the feasibility of time-modulating materials to control light.

Levitated nanoparticles can now be cooled to the motional ground state in two dimensions. This advance could enable a new generation of macroscopic quantum experiments.

A quantum engineering technique powered by disorder offers access to local correlation functions down to single-site resolution in nuclear spin ensembles, allowing the study of both spin and energy hydrodynamics.

Research in the past few decades has uncovered powerful generalities in the structure of many natural and built networks. Now, a study describes how certain structural properties of networks may cause them to endure or collapse over time.

Developing tissues undergo collective cell movement and changes to their material properties, such as flow characteristics. Now tissue fluidity is linked to tissue growth.

Time crystals are a new state of matter. Conventional crystal properties are periodic in space, while the properties of a time crystal are periodic in time. A continuous quantum time crystal has recently been realized, and now, using optically driven many-body interactions in a nano-mechanical photonic metamaterial, a classical continuous time crystal has been created.

It’s a long-standing theoretical prediction that mutual information in locally interacting, many-body quantum systems follows an area law. Using cold-atom quantum-field simulators on an atom chip to measure the scaling of von Neumann entropy and mutual information, that prediction is now proved true.

Spin liquids are predicted to emerge in materials that combine strong electronic correlations with geometric frustration. Evidence has now been found for a spin liquid state in the triangular-lattice material NaRuO₂.

Layering quantum materials can produce interesting phenomena by combining the different behaviour of electronic states in each layer. A layer-sensitive measurement technique provides insights into the physics of a magnetic topological insulator.

The performance of superconducting devices is affected by the generation and relaxation of excitations called quasiparticles. A scanning tunnelling microscope can controllably inject quasiparticles so their dynamics can be better understood.

The spontaneous topological Hall effect, combining non-coplanar antiferromagnetic order with finite scalar spin chirality in the absence of a magnetic field, is now experimentally demonstrated for the triangular lattice compounds CoTa₃S₆ and CoNb₃S₆.

Glasses relax internally even when their structure is frozen. Observations of a two-dimensional glass former now show that although structure relaxation freezes with the glass transition, non-constrained bonds survive; this accounts for persisting internal relaxation.

Reliably probing rejuvenation and memory effects in spin glasses by means of simulations is difficult. Now, a state-of-the-art numerical study shows that at least three different length scales play a crucial role in aging dynamics of spin glasses.

So far, a continuous time crystal has only been implemented on a quantum system. Optically driven many-body interactions in a nanomechanical photonic metamaterial now allow the realization of a classical continuous time crystal.

Some topological boundary states are symmetry protected. Experiments with photonic lattices now show that the protection via sub-symmetry is enough to ensure topological modes, even if the full symmetry and topological invariant are destroyed.

A temporal version of Young’s double-slit experiment shows characteristic interference in the frequency domain when light interacts with time slits produced by ultrafast changes in the refractive index of an epsilon-near-zero material.

Optically trapped and levitated nanoparticles can be used to study macroscopic quantum effects, but fully controlling their motion is difficult. Now, all six roto-translational degrees of freedom have been cooled, although not to the quantum ground state.

A levitated nanoparticle in an optical cavity has been cooled to its motional ground state in two degrees of freedom at the same time. Control of the cavity properties also enabled the observation of the transition from 1D to 2D ground-state cooling.

Synthetic dimensions can introduce band properties without a periodic structure in real space, but they have largely been studied in linear systems. A study using an optical resonator has now shown non-linear soliton states in synthetic frequency space.

The scaling of entanglement entropy and mutual information is key for the understanding of correlated states of matter. An experiment now reports the measurement of von Neumann entropy and mutual information in a quantum field simulator.

Probing strongly interacting quantum systems with high spatial resolution can be challenging. An experiment now uses disorder in nuclear spin chains as a local probe to investigate spin and energy hydrodynamics.

Despite looking highly irregular, most real-world networks exhibit natural stability to external perturbations. A study of the properties of the stability matrix of networks now sheds light on the principles underlying this emerging stability.

Tests of the predictions of the renormalization group in biological experiments have not yet been decisive. Now, a study on the collective dynamics of insect swarms provides a long-sought match between experiment and theory.

Developing tissues undergo rheology transitions that are often linked to cell–cell adhesion. Now, tissue fluidity is linked to interkinetic nuclear movements and tissue growth.

Elastoviscoplastic fluids combine solid- and liquid-like behaviour depending on applied stress. Simulations of elastoviscoplastic fluids at high Reynolds number now show that plasticity plays a key role in the turbulent flows seen in these systems, leading for example to intermittency.

The unit one is a necessary part of any system of units but debate concerning its proper treatment in science and technology continues. Richard Brown enumerates its uses.