Articles in 2011

The final bids are in to host a major radio telescope, the Square Kilometre Array.

For an important class of liquids, relaxation dynamics are constrained by a surprisingly simple scaling relationship between density and temperature. It seems that thermodynamics holds the key to pinning down the exponent.

A demonstration of the ability to produce arbitrary-shaped electron bunches from an ultracold gas represents an important step towards studying ultrafast molecular processes in laboratories around the world.

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.

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.

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.

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.

Quantum states of light could be a better probe for materials than classical states, but they are hard to generate in the laboratory. A scheme that combines large amounts of data with sophisticated theoretical analysis gets around this limitation.

Generating intense bursts of high-energy radiation usually requires the construction of large and expensive facilities, such as free-electron lasers, which are based on conventional particle accelerators. Laser-driven accelerators offer a cheaper and smaller alternative, and they are now capable of generating intense bursts of gamma-rays.

Experiments that exploit non-classical properties of light promise to provide unique information about many-body systems. The limited availability of non-classical light sources, however, makes their implementation challenging. A method to calculate the quantum-optical response of a material from signals measured by using coherent-light excitation might provide an alternative route.

The radiation produced when an intense laser interacts with a solid target could provide a cheaper source of X-rays to synchrotrons and free-electron lasers. But they can also produce short bursts of gamma rays, whereas synchrotrons do not.

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.

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.

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.