Research articles

Shor’s quantum algorithm factorizes integers, and implementing this is a benchmark test in the early development of quantum processors. Researchers now demonstrate this important test in a solid-state system: a circuit made up of four superconducting qubits factorizes the number 15.

It is known that graphene exhibits natural ripples with characteristic lengths of around 10 nm. But when it is stretched across nanometre-scale trenches that form in a reconstructed copper surface, it develops even tighter corrugations that cannot be explained by continuum theory.

Doping a topological insulator with manganese makes it magnetic. Moreover, decreasing the concentration of Dirac fermions in a Mn-doped topological insulator with an electric field increases the strength of its magnetic characteristics—a trait that could be valuable to the use of topological insulators in the development of spintronics.

The ability to modify a material’s magnetization with an electric field could enable lower-power electronic devices. Such ‘magnetoelectric’ behaviour is usually only seen at the interface between magnetostrictive and electrostrictive materials, but has now been observed in the bulk of single-component rare-earth ferrites.

When electrons are accelerated to near light-speeds through an overdense plasma by an intense laser beam, the usually opaque plasma becomes optically transparent. High-speed laser experiments provide unprecedented insight into the dynamics of this process.

Spin–orbit interaction induces spin-polarization decay in semiconductor quantum wells. But this decay can be suppressed in favour of a helical spin mode by tuning the interaction. Optical pump–probe measurements provide direct evidence of the resulting helix—a signature that has so far only been inferred from transport measurements.

Decreasing the doping of a cuprate superconductor below a certain critical value causes its critical temperature to fall, however the reason for this has been unclear. Sensitive measurements of the Nernst effect in yttrium barium copper oxide suggest it is the result of competition with an emerging stripe phase.

When a low-viscosity fluid penetrates a fluid of higher viscosity confined by parallel plates, finger-like patterns propagate at the interface between the two fluids. Experiments now show that tapering the fluid cell can suppress this instability - providing interfacial control via a simple change in geometry.

Quantum discord is the total non-classical correlation between two systems. This includes, but is not limited to, entanglement. Photonic experiments now demonstrate that separable states with non-zero quantum discord are a useful resource for quantum information processing and can even outperform entangled states.

Entanglement is not the only type of quantum correlation. Quantum discord is a broader measure of such non-classical interactions. An experimental investigation now shows how quantum discord can be consumed to encode information, even in the absence of entanglement.

In most electrical conductors, heat is transported by charge carriers and so both usually flow in the same direction; but in two-dimensional electron systems subject to strong magnetic fields, certain fractional quantum Hall states can cause charge and heat to flow in opposite directions.

In metals, the Coulomb potential of charged impurities is strongly screened, but in graphene, the potential charge of a few-atom cluster of cobalt can extend up to 10 nm. By measuring differences in the way electron-like and hole-like Dirac fermions are scattered from this potential, the intrinsic dielectric constant of graphene can be determined.

Two-dimensional Bose fluids—such as liquid-helium films, or confined ultracold atoms—cannot form a condensate, but become superfluid instead. Frictionless flow, proving superfluid behaviour, has now been observed in an ultracold two-dimensional Bose gas that is stirred with a laser beam.

Short-lived kinetic states between equilibria are difficult to access experimentally, despite being crucial in many dynamical processes. Single-molecule experiments demonstrate that an extended fluctuation relation allows extraction of the free energies of these metastable states under non-equilibrium conditions.

Chemical reactions between a single trapped ion and a condensate of ultracold neutral atoms are investigated by controlling the quantum states of both ion and atoms—revealing the effect of the hyperfine interaction on the reaction dynamics.

In systems of oscillators, phase-locking behaviour can, in theory, coexist with incoherent dynamics—invoking the fabled chimera state. Now, experimental realization of a coupled-map lattice reveals dynamical states displaying coexisting spatial domains of coherence and incoherence.

Chimera states describing the stable coexistence of synchronous and incoherent dynamics have so far only been realized numerically. An experimental demonstration of these states in a network of discrete chemical oscillators reveals behaviour that differs from that predicted by existing phase-oscillator models.

An ideal amplifier has low noise, operates over a broad frequency range and has large dynamic range. A superconducting-resonator-based amplifier that combines all of these qualities is now demonstrated. The concept is applicable throughout the microwave, millimetre-wave and submillimetre-wave bands and can achieve a noise limit very close to that set by quantum mechanics.

Magnetic vortices confined to thin films gyrate with a dynamics determined by the vortex–core polarity, which switches when the gyration is fast enough. Fine-tuning these core-reversal oscillations reveals rich nonlinear behaviour, including commensurate and chaotic states.

Tissue growth and regrowth rely on the collective migration of sheets of cells. Gradients in tension established through intercellular forces guide this migration, but the mechanism driving the gradients has remained unclear. Innovative experiments now reveal their origin—in a mechanical wave set up by sequential cell reinforcement and fluidization.