Volume 7 Issue 12, December 2011

Investment in science must be part of Europe's plan to rebuild its economies.

Fibre networks inspire an update to a century-old criterion for mechanical integrity — showing that a little bending resistance can go a long way.

Monolayer graphene is a semimetal with no bandgap, and bilayer graphene is a semiconductor with a tunable gap. A trio of studies now shows that trilayer graphene can be either, depending on how its layers are stacked — behaviour that could support exotic new electronic states.

The realization that primordial black holes produce oscillations when they pass through stars brings us one step closer to observing traces of this dark-matter candidate that formed in the early Universe.

An open quantum system loses its 'quantumness' when information about the state leaks into its surroundings. Researchers now show how this decoherence can be controlled between two incompatible regimes in the case of a single photon.

Defects in diamond crystals possess rare physical properties that can enable new forms of technology. Unlocking this potential requires rapid quantum-state measurement, a 'quantum snapshot', which has now been achieved.

An open quantum system loses its ‘quantumness’ when information about the state leaks into its surroundings. Researchers now control this so-called decoherence in a single photon. By rotating an optical filter, the information flow between the photon and its environment can be tuned. This concept could be harnessed for future quantum technologies.

At the nanoscale, the conductance of a coherent conductor is reduced by the back-action of the circuit in which it is inserted. The effect has been primarily studied for cases where it is small, but these authors explore the regime of strong back-action—with conductance reductions of up to 90%—and propose a generalized expression for the conductance of quantum channels embedded in linear circuits.

Helical Dirac fermion states in topological insulators could enable dissipation-free spintronics and robust quantum information processors. A study of the influence of disorder on these states shows that although they are resilient against backscattering by magnetic impurities, fluctuations caused by charge impurities could cause problems for such applications.

Monolayer graphene has no electronic band gap. Bilayer graphene does, and can be controlled by an electric field. And for trilayer graphene, infrared transmission measurements indicate both situations are possible depending on the stacking of the layers.

The electronic properties of graphene depends on how many layers are involved. Monolayer graphene is a zero-gapped semi-metal. Bilayer graphene is a small-gapped semiconductor. Magnetotransport measurements indicate trilayer graphene can be both, depending on its stacking.

Soon after the isolation of graphene, it was discovered that the charge carriers in monolayer and bilayer sheets exhibit exotic Berry phases of π and 2π respectively. Now, magnetotransport measurements suggest the sequence continues in trilayer graphene, with charge carriers that exhibit a Berry phase of 3π.

Disorder-induced Anderson localization usually causes conducting materials to become insulating at low temperature. Graphene is a notable exception. But by increasing the carrier density in one graphene layer, a metal–insulator transition can be induced in an isolated second layer stacked above it.

‘Squeezed light’ enables quantum noise in one aspect of light to be reduced by increasing the noise, or more accurately the quantum uncertainty, of a complementary aspect. This has now been used to push the detectors at the heart of the GEO600 gravitational wave observatory to unprecedented levels of sensitivity.

Constraint-satisfaction problems are among the computationally hardest tasks: solutions are efficiently checkable, but no efficient algorithms are known to compute those solutions. Fresh insight might come from physics. A study mapping optimization hardness onto the phenomena of turbulence and chaos suggests that constraint-satisfaction problems can be tackled using analog devices.

So-called topological properties can make quantum systems robust to a wide class of microscopic perturbations. Theoretical work now shows that topological features and phenomena occur not only in closed systems, but also in open quantum systems with appropriately engineered dissipation.

Understanding the origin of colossal magnetoresistance in the manganites has proved to be one of the more difficult challenges in condensed-matter physics. An unexpected discovery of polarons in the metallic ground state of bilayer manganites could be an important clue.

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.