Research articles

Transforming a quantum system with high fidelity is usually a trade-off between an increase in speed—thereby minimizing decoherence—and robustness against fluctuating control parameters. Protocols at these two extreme limits are now demonstrated and compared using Bose–Einstein condensates in optical traps.

The unavoidable coupling between a quantum state and its environment leads to decoherence. Weak measurements—indirectly observing a quantum state without disturbing it—are now shown to be a useful tool for reducing or even nullifying the effects of decoherence.

So-called topological defects appear in various forms, be it as monopoles, cosmic strings, vortex lines or domain walls. This work suggests that such localized entities can be put in non-local superpositions, and describes the decoherence behaviour of such quantum states.

An optical technique based on Doppler velocimetry reveals important aspects of the physics underlying the propagation of spin polarization in a two-dimensional electron gas. The spin mobility is shown to track the high electron mobility, but coherent spin precession is lost at temperatures near 150 K, posing a challenge for future spintronics devices.

An optically trapped colloidal particle serves as the first realization of a stochastic thermal engine, extending our understanding of the thermodynamics behind the Carnot cycle to microscopic scales where fluctuations dominate.

It has long been debated whether it is possible to approach a zero-temperature metallic state in a two-dimensional system. A study of the electrical characteristics of arrays of superconducting islands of varying thickness and spacing on a normal metal film suggests it is.

When an intense laser pulse hits a flat metal foil, it ejects a spray of high-energy protons. Laser irradiation of a curved foil covering the tip of a hollow cone focuses the protons to intensities that could be useful for generating extreme states of matter.

Electromagnons are excitations that exhibit both electric and magnetic dipole moments, and are expected to enhance the coupling of magnetization and polarization in multiferroic materials. The identification of electromagnons in a perovskite helimagent may be useful in the development of ways to manipulate light.

Manipulating the electrons trapped in quantum-dot pairs is one possible route to quantum computation. Translating this idea to three quantum dots would enable a whole host of extended functionality. Researchers now generate and manipulate coherent superpositions of quantum states using the spins across three electrical-gate-defined dots.

The discovery that potassium-doped iron selenide undergoes phase separation into a defect-free superconducting phase and an iron-vacancy-ordered insulating phase resolves many questions about the unusual behaviour of this iron-based superconductor.

Experimental progress has made it possible to load fermionic atoms into higher orbital bands. Such systems provide a platform for studying quantum states of matter that have no prior analogues in solid-state materials. This theoretical study predicts a semimetallic topological state in these systems, which can be turned into a topological insulating phase.

Laser-driven proton accelerators could enable more effective cancer treatment, but to fulfil this function proton beams with a higher energy and narrower energy spread will need to be produced. Discovery of a laser–plasma acceleration mechanism that generates 20 MeV proton beams with a 1% spread is a promising step.

The controlled creation of one-dimensional conductive channels at the cores of topological defects in the multiferroic material BiFeO₃ demonstrates that such defects can drive metal–insulator phase transitions, and might provide a route towards high-density information storage.

Photoelectron spectroscopy is an invaluable tool for better understanding the energy levels of molecules. However, many levels remain hidden because of transition selection rules or a high density of states. Using X-rays to excite core–shell electrons and monitoring their Auger decay enables the extraction of previously hidden molecular-potential curves.

The behaviour of molecules and solids is governed by the interplay of electronic orbitals. Superfluidity, in contrast, is typically considered a single-orbital effect. Now, a combined experimental and theoretical study provides evidence for a multi-orbital superfluid, with a complex order parameter, occurring in a binary spin mixture of atoms trapped in an hexagonal optical lattice.

Glass-forming liquids are generally thought to relax through a collective rearrangement of domains, correlated over a length scale that increases with decreasing temperature. A numerical study now reveals a surprising twist to the story, claiming that relaxation depends non-monotonically on temperature.

In fibre networks, mechanical stability relies on the fibres’ bending resistance—in contrast to rubbers, where entropic stretching is the key. The extent to which the mechanics of fibre networks is controlled by bending is, however, an open question. The study of a general lattice-based model of fibrous networks now reveals two rigidity critical points, one of which controls a rich crossover from stretching-dominated to bending-dominated behaviour.

A quantum particle can tunnel through an energy barrier that it would otherwise be unable to surmount. This phenomenon has an important role in atomic processes such as ionization. Researchers now use an attosecond ‘clock’ to take a precise look at the dynamics of this process and identify the trajectory taken by the escaping electron.

In strong magnetic fields, clean two-dimensional electron systems support fractional Hall states that exhibit isotropically vanishing longitudinal resistance. At low field these states disappear and an anisotropic stripe phase emerges. And in between, contrary to expectation, these states can coexist.

Multiple valleys in the electronic structure of certain crystal lattices could enable the development of so-called valleytronic devices. But to do so, the degeneracy of these valleys must be lifted. Measurements of the anisotropic magnetoelectric response of bismuth suggest that its three-fold valley degeneracy breaks spontaneously at low temperatures and high fields.