Articles in 2008

Many studies on the properties of the recently discovered ferropnictide superconductors report seemingly contradictory results. A theoretical study suggests that these contradictions might be resolved by considering such materials as having a strongly magnetic ground state whose domain boundaries fluctuate, preventing their experimental detection.

A general approach to simplifying quantum logic circuits—the ‘programs’ of quantum computers—is described and demonstrated on a platform based on photonic qubits.

An array of superconducting nanocircuits has been designed that provides built-in protection from environmental noises. Such ‘topologically protected’ qubits could lead the way to a scalable architecture for practical quantum computation.

High-resolution electron microscope images collected in real time demonstrates the occurrence of multiple intermediary phases during the crystallization of a metal phosphate. The observations represent the first atomic-scale demonstration of Wilhelm Ostwald’s ‘rule of stages’ proposed over a century ago.

An accurate determination of the size and diffusion length of excitons generated with single-walled nanotubes supports the Wannier–Mott picture of their behaviour, and improves the outlook for the use of nanotubes in optoelectronics and biosensing applications.

Analysis of the ejection of electrons in a plane perpendicular to an incident electron beam reveals unexpected differences between the ionization behaviour of atoms and molecules. For molecules that have nuclei at their centres of mass, the angular distribution of emitted electrons is similar to that of atoms. But for those that don’t, the shape of this distribution is qualitatively different.

In many real-world processes that can be mapped onto complex networks—from cell signalling to transporting people—communication between distant nodes is surprisingly efficient, considering that no node has a full view of the entire network. A framework sets out to explain why ‘navigability’ is so efficient in these networks.

An algorithm that reconstructs the structure of an object in flight from the diffraction pattern generated by exposing it to an ultrashort burst of X-rays should enhance the potential of free-electron lasers for studying individual molecules, virus and nanoparticles.

Optical lattice clocks, in which trapped atoms serve as a frequency reference, are promising candidates for next-generation atomic clocks. Depending on whether bosons or fermions are loaded into the lattice, fundamentally different design principles apply, as has now been shown.

The tendency of small objects to stick together as they come into contact is a commonly observed phenomenon. Yet the interactions that govern this behaviour can be complex. A systematic study of the variation in the force between a particle and a solid surface as they are brought together finds many parallels with the characteristics of glassy and granular systems.

Electron microscopes are regularly used to resolve atoms in solid samples. It turns out that they can also be used to image atoms in a Bose–Einstein condensate—remarkably, without destroying the coherent properties of the condensate.

It is already known that the theory of quantum entanglement shares some analogies with the laws of thermodynamics. Now a rigorous and general link between the two fields has been established.

The computational capability of the brain remains a mystery. Some insight might come from a series of experiments in which cultures of living neurons are patterned in a way to form functional logic devices.

Coupling of the Rydberg states of an ensemble of rubidium atoms gives rise to a d.c. Kerr effect that is six orders of magnitude greater than in conventional Kerr media. Such phenomena could enable the development of high-precision electric field sensors and other nonlinear optical devices.

Impurity centres in diamond have recently attracted attention in the context of quantum information processing. Now their use as magnetic-field sensors is explored, promising a fresh approach to single-spin detection and magnetic-field imaging at the nanoscale.

Interactions between photons are typically extremely weak. But when light pulses are confined to an optical waveguide and manipulated with nearby cold atoms, strongly interacting photons can be created that may even undergo crystallization, as is now shown theoretically.

The coupling of a quantum system to its environment is usually associated with the unwanted effect of decoherence. But theoretical work shows that with suitably engineered couplings, dissipation can drive a system of cold atoms into desired many-body states and quantum phases.

Analysis of how condensation of an ensemble of bilayer excitons reorganizes the low-energy degrees of freedom of its constituent fermions suggests it should be possible to generate a dissipationless superflow in such a system.

Improvements in the microwave output efficiency of MgO-based magnetic tunnel junctions brings them a step closer to practical applications and enables greater insight into the physics of spin transfer in such devices.

State-of-the-art simulations of disorder-induced trapping of light in inverted opals provides a basis for a definitive identification, and potential use, of the three-dimensional Anderson localization of light.