Articles in 2021

Excitons have been predicted to form spontaneously—without external excitation—in some materials. Low-temperature ARPES measurements on Ta₂NiSe₅ now provide evidence for such an excitonic insulator and for so-called preformed excitons.

A class of synthetic microswimmers self-assembled from alkane oil drops in a surfactant solution offers a rechargeable platform for studying how microorganisms exploit flagellar elasticity to move around.

Many quantum machine learning algorithms have been proposed, but it is typically unknown whether they would outperform classical methods on practical devices. A specially constructed algorithm shows that a formal quantum advantage is possible.

Macroscale patterns seen in biological systems such as animal coats or skin can be described by Turing’s reaction–diffusion theory. Now Turing patterns are shown to also exist in bismuth monolayers, an exemplary nanoscale atomic system.

Measurement-based quantum computing performs quantum gates on entangled states without difficult multi-qubit coherent dynamics. A set of gates sufficient for universal quantum computing has now been implemented on a programmable optical platform.

Insights into the structure of the Vlasov equation that governs the evolution of collisionless plasmas from observations have been limited. Now the spatial gradient term for electrons is analysed with recent data from the MMS mission.

The ATLAS Collaboration reports a measurement of the ratio of the decay rates of W bosons to τ leptons and muons, in agreement with universal lepton couplings as postulated in the standard model of particle physics.

The ATLAS experiment at the Large Hadron Collider reports a search for charged-lepton-flavour violation in decays of Z bosons into a τ lepton and an electron or muon of opposite charge.

Entanglement is central to theories of quantum many-body systems but is very resource intensive to measure. A protocol based on a quasilocal parametrization of physical states allows entanglement structures to be studied using very few measurements.

A study of the dynamics of polymer translocation through synthetic nanopores provides a direct observation of tension propagation—a non-equilibrium description of the process of unfolding that a polymer undergoes during translocation.

Relativistic mirrors are a promising tool to reach laser intensities up to the Schwinger limit. Such a mirror is created in ultra-intense laser–solid interactions, and its temporal and spatial effects on the reflected laser beam are characterized.

Learning the Hamiltonian of a complex many-body system is hard, but now there is proof that it can be done in a way where the number of required measurements scales as a polynomial of the number of particles.

Self-propelled particles are shown to orient themselves towards areas of high density, phase separating into fluid-like clusters. This behaviour is unique to active systems, forming a distinct class of motility-induced phase separation.

Alkali metals at high pressures have a liquid–liquid transition that is difficult to study in detail. Numerical calculations now suggest that the higher-pressure state is an electride liquid, in which electrons behave like localized anions.

Chains of magnetic atoms on the surface of a superconductor are shown to have topologically non-trivial bands that could host Majorana bound states.

Topologically protected charge transport, known as Thouless pumping, is realized with cold atoms trapped in quasi-periodic disordered potentials. The pumping is disorder-dependent, illustrating the influence of disorder on the topological properties.

Quantum systems make it challenging to determine candidate Hamiltonians from experimental data. An automated protocol is presented and its capabilities to infer the correct Hamiltonian are demonstrated in a nitrogen-vacancy centre set-up.

A two-fold rotational symmetry is observed in the superconducting state of NbSe₂. This is strikingly different from the three-fold symmetry of the lattice, and suggests that a mixed conventional and unconventional order parameter exists in this material.

Measurements of the proton’s spin structure in experiments scattering a polarized electron beam off polarized protons in regions of low momentum transfer squared test predictions from chiral effective field theory of the strong interaction.

A computational framework draws analogy with foams to offer a comprehensive picture of how cell behaviours influence fluidization in embryonic tissues, highlighting the role of tension fluctuations in regulating tissue rigidity.