Articles in 2010

Atomic transitions afford a convenient way of storing quantum bits. However, there are few ground-state transitions suitable for use with light at telecommunication wavelengths. Now, researchers show that ensembles of cold rubidium atoms not only make good quantum memories, but can also noiselessly convert the emitted photons into and out of the telecoms band.

Diffraction conventionally limits the length scale on which spins can be optically probed. A new technique that uses doughnut-shaped beams of light to select just one nitrogen-vacancy centre, by suppressing the fluorescence from those around it, enables single-spin detection, imaging and manipulation with nanoscale resolution.

Extensive data sets of trajectories of mobile-phone users provide a new basis for modelling human mobility. Random-walk models can capture some aspects, but go only so far. Now, two governing principles for human mobility are proposed, exploration and preferential return, paving the way to a more appropriate microscopic model for individual human motion.

In one-dimensional systems, phase transitions at finite temperature are deemed impossible, because long-range correlations are destroyed by thermal fluctuations. Theoretical work now shows that, nonetheless, a phase transition at finite temperature can occur in a one-dimensional gas of weakly interacting bosons in a random environment

Quantum critical points in many-body systems are characterized by the appearance of long-range entanglement. These subtle quantum correlations are known to be extremely fragile with respect to thermal noise. But theoretical work now shows that, unexpectedly, another classical disturbance, the ubiquitous 1/f noise, does preserve the critical correlations.

Real-space mapping of the quantum Hall state at the Dirac point in epitaxial graphene reveals unexpected localized lifting of the degeneracy of this level. This could be the result of moiré interference caused by the twisting of the top layer with respect to underlying layers, suggesting possible new ways to understand and control the unusual properties of graphene.

An optical cavity coupled to a micrometre-sized mechanical resonator offers the opportunity to see quantum effects in relatively large structures. It is now shown that a variety of coupling mechanisms enable investigation of these fascinating systems in a number of different ways.

It’s long been known that the presence of grain boundaries between misaligned crystallites limits the supercurrent in a superconductor. A microscopic-based theory now reveals that charge inhomogeneities build up at a grain boundary to block the superconducting current.

The properties of electric conductors change markedly once quantum phenomena become relevant. So far, work on quantum coherent electron transport has largely focused on static properties, but new theoretical work now looks at such phenomena in the regime of fast alternating currents.

Organic semiconductors are attractive candidates for spintronics applications because of their long spin lifetimes. But few studies have investigated how to optimize the injection of spin into these materials. A new study suggests that the metal/organic interface is key.

At absolute zero temperature, exotic phases of matter can be found near a quantum critical point. If geometric frustration is also present, as happens in columbite, the extra quantum fluctuations lead to five distinct states of matter.

Although the formation of beads on filaments of saliva drawn between two solid surfaces is familiar to most people, the precise mechanism responsible for such behaviour has been hotly debated. Simulations reveal that inertial effects play a pivotal role in this process.

It is widely expected that the properties of composite fermions should be independent of those of the electrons and flux quanta from which they emerge. Measurements of anisotropic transport in AlAs quantum wells suggest this is not the case.

In a quantum computer, the data carriers (or qubits) must be well isolated from their environment to avoid information leakage. At the same time they have to interact with one another to process information. A proposed platform based on spin qubits connected through arrays of nanoelectromechanical resonators should be able to reconcile these conflicting requirements.

Despite all of the fundamental research carried out on them, artificial atoms continue to be a source of surprise. The intersection between the electrons in a quantum dot and a nearby sea of electrons can create unusual many-body states. A spectroscopic study now makes these states observable.

Similar to atoms in cold gases, exciton–polaritons in semiconductor microcavities can undergo Bose–Einstein condensation, but under non-equilibrium conditions. Now, quantized vortices and persistent currents — hallmarks of superfluid behaviour — have been observed in such condensates.

Networks have been widely explored in the context of classical statistical mechanics. But when quantum effects are added, qualitatively different behaviours emerge, even for the simplest cases.

Large clusters of galaxies are cosmologically significant, and their thermal history is determined by magnetic fields. Simulations show that the magnetic-field lines in the Virgo cluster, rather surprisingly, are oriented radially. This would explain the observed ridged structure. Moreover, the model may explain why some clusters have not cooled as expected.

Non-local transport measurements on mercury telluride quantum wells show clear signatures of the ballistic spin Hall effect. The ballistic nature of the experiment allows the observed effect to be interpreted as a direct consequence of the band structure of these semiconductor nanostructures, rather that being caused by impurity scattering.

Differences in diffusion constants of activator and inhibitor species can destabilize biological and chemical processes, leading to the spontaneous emergence of periodic spatial patterns. A general framework now provides the tools for studying such so-called Turing patterns in systems organized in complex networks.