Volume 6 Issue 11, November 2010

Fifty years ago, Abdus Salam envisaged a 'world centre' for theorists. Now the institute that he founded is adapting to a changing world and to changing ways of doing science.

A school on computational materials science that drew expert teachers and talented participants marks a new approach to the development of research in Africa.

The Nobel Prize in Physics 2010 has been awarded to Andre Geim and Konstantin Novoselov "for groundbreaking experiments regarding the two-dimensional material graphene".

The quantum kagome lattice is a fundamental but experimentally elusive frustrated magnet. Neutron spectroscopy now reveals the ground state and elementary excitations of a deformed kagome lattice in which the quantum spins form an exotic pinwheel valence-bond state.

Converting data-carrying photons to telecommunication wavelengths enables distribution of quantum information over long distances.

Measurement-based quantum computation with an Affleck–Kennedy–Lieb–Tasaki state is experimentally realized for the first time.

Quantum mechanics predicts that measurements on spatially separated particles can yield non-local correlations. This is well established but defies intuition about space and time. The concept of 'steering' might help us to understand quantum non-locality better.

Erwin Schrödinger introduced in 1935 the concept of ‘steering’, which generalizes the famed Einstein–Podolsky–Rosen paradox. Steering sits in between quantum entanglement and non-locality — that is, entanglement is necessary for steering, but steering can be achieved, as has now been demonstrated experimentally, with states that cannot violate a Bell inequality (and therefore non-locality).

One-way quantum computing requires an entangled multiqubit system. So-called cluster states have been proposed to provide this resource, but they are difficult to generate. An alternative that uses the ground state of a one-dimensional chain of spins is now experimentally realized and used to construct a quantum logic gate.

When doped with copper, the topological insulator Bi₂Se₃ becomes superconducting. But for new physics and applications the search is not for just any superconductor; the material must retain its topological character. And indeed that is the case with doped Bi₂Se₃.

Long-lived polariton condensates can propagate well beyond the area of their initial excitation while still maintaining spatial coherence. This enables direct and controllable manipulation of the condensate wavefunction.

Single crystals of a two-dimensional quantum spin system with geometric frustration lead to the observation of a ‘pinwheel’ valence-bond ground state. In this case, the distortion of the ideal kagome lattice structure helps to stabilize the quantum spin state.

Monitoring the photocurrent generated as a laser scans across a graphene field-effect device subjected to low temperature and high magnetic fields enables the spatial distribution of Landau levels across a graphene sheet to be mapped. This in turn allows the relative contribution of bulk and edge states to the macroscopic electrical characteristics of these devices to be determined.

A pure spin current has no net charge current and is therefore difficult to detect. A new technique that takes advantage of nonlinear optical effects can measure pure spin currents non-invasively, non-destructively and in real-time.

The experimental demonstration of heat currents driving the injection of spins from a ferromagnetic into a non-magnetic metal establishes a new source of pure spin currents. The approach might provide an alternative mechanism for switching processes in memory devices and for other ‘spintronics’ applications.

Introducing a phase shift between diffracted and undiffracted light from a sample is one of the oldest techniques for generating phase contrast in optical microscopy. A similar approach should help improve the contrast and clarity of images collected by scanning X-ray microscopy.

Spreading of information, ideas or diseases can be conveniently modelled in the context of complex networks. An analysis now reveals that the most efficient spreaders are not always necessarily the most connected agents in a network. Instead, the position of an agent relative to the hierarchical topological organization of the network might be as important as its connectivity.

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.

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

Quantitative measurements that establish the existence and evolution of quasiparticles across the whole phase diagram of a cuprate superconductor help to distinguish the many theoretical models for high-temperature superconductivity.

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.

The energy potentials created by laser light can trap atoms. An analogous effect that traps electrons in solid-state systems is now proposed. The electron traps are created in quantum wells and wires in the presence of quasiparticles composed of two electrons and a hole. The idea could lead to advances in ultrafast optical and new optoelectronic devices.