Volume 8 Issue 8, August 2012

Graphene could offer an efficient and controllable interface between nanoscale optics and electronics, and promises a new generation of optoelectronic devices.

Cells migrate en masse to generate and renew tissue — but inadequate resolution and incompatible timescales obscure the mechanism behind this migration. A unique approach reveals that stress mediates collective motion by propagating in a wave from the leading edge to the population centre.

Supersymmetric particles are prime candidates to make up the dark matter of the Universe — yet the lack of evidence for them so far from the Large Hadron Collider could force a rethink.

Atomic-resolution differential phase-contrast imaging using aberration-corrected scanning transmission electron microscopy now provides a sensitive probe of the electric field associated with individual atoms.

Is it possible to deduce the number of dimensions of a completely unknown system only from the results of measurements performed on it? So-called dimension witnesses allow such an estimation, and are now experimentally demonstrated using pairs of entangled photons.

Hilbert space is made up of a potentially infinite number of dimensions that correspond to all the parameters needed to fully define a system. The idea is seen as an important resource for quantum information processing. A technique for estimating the number of dimensions in an unknown system based on the results of measurements performed on it—a so-called dimension witness—is now experimentally demonstrated.

Nuclear spin is seen as a robust qubit. Electrons can be used to ‘read’ to the nuclear state, but their presence causes decoherence. Researchers now show that this problem can be circumvented using a temporary spin state, thus enabling entanglement of the nuclear state at unprecedented speeds.

Density functional theory provides a powerful framework for probing electronic structure in many-body systems. A new functional for particles interacting via short-range potentials extends its applicability to ultracold atoms in optical lattices.

How and why Fermi arcs—disconnected segments of the Fermi surface—emerge in the pseudogap phase of cuprate superconductors is a mystery. A technique for analysing angle-resolved photoemission spectroscopy data that removes momentum broadening effects suggests these arcs do not reflect true Fermi surface states, which would explain why they do not form continuous loops.

A technique capable of detecting the electric field associated with individual atoms is now demonstrated. Atomic-resolution differential phase-contrast imaging using aberration-corrected scanning transmission electron microscopy provides a sensitive probe of the gradient of the electrostatic potential in a crystal lattice.

Breaking the time-reversal symmetry of the surface states of topological insulators is predicted to produce many exotic and potentially useful phenomena. Spin-resolved angle-resolved photoemission spectroscopy spectra reveal that magnetic dopants can induce such symmetry breaking in Be₂Se₃ thin films.

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.

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.