Articles in 2010

Artificial magnetic materials may lead to studies of the thermodynamics of arbitrarily designed lattices. Unfortunately, none of the proposed materials has achieved its ground state through thermodynamic equilibrium as real materials do — until now.

Topological insulators have a conducting surface on which spin currents are not easily scattered, although the addition of magnetic impurities does affect electronic behaviour. But is this situation unique? Graphene comes to mind.

Increasing the power of ultra-high-intensity lasers requires crystal amplifiers and metre-scale optical compression gratings that are ever more difficult to build. Simulations suggest that Raman amplification in a plasma could permit the generation of laser intensities many orders of magnitude higher than currently possible.

Around the world, in developed and developing countries, there is reluctance to commit to the alleviation of climate change. But investment in clean energy is growing.

The search for the Higgs boson could soon prove successful. Although the particle bears the name of a single physicist, many more were involved in devising the theory behind it — so which of them should share a potential Nobel Prize?

In the pseudogap phase of a high-temperature cuprate superconductor, conflicting evidence from different experiments points to a competing state or a precursor-to-superconductivity state. One single experiment now determines that both states exist.

A potentially critical limiting factor in the use of free-electron lasers to determine the structure of organic molecules is the damage the procedure may cause. A model based on coherence theory and quantum electrodynamics suggests that it should be possible to reconstruct a molecule’s structure from the X-ray data obtained as it undergoes damage.

A study of autoresonant behaviour in a superconducting quantum pendulum reveals that fluctuations, both quantum and classical, only determine the initial oscillator motion, not its subsequent dynamics.

A genetic-algorithm approach to analysing quantum oscillations in a high-temperature superconductor reveals that quasiparticles behave as nearly free spins—split into spin-up and spin-down populations, known as the Zeeman effect.

Birefringent particles manipulated with an optical torque wrench exhibit strongly nonlinear, ‘excitable’ behaviour similar to that governing the firing of neurons. This technique could be used to detect small perturbations in the local environment of such a particle.

Light-emitting quantum dots are usually assumed to behave as perfect point-source emitters. It is now found that this assumption breaks down when quantum dots are placed near structures that support nanoscale optical modes — information that could be useful in building better nanophotonic devices.

Optical control over electron spins embedded in semiconductor structures is an efficient way of manipulating quantum information. But a fully fledged quantum information processor will require control over two-spin states. This has now been demonstrated, including the implementation of ‘ultrafast’ two-qubit gate operations that take less than a nanosecond.

Topological insulators are bulk insulators beneath conducting surface states with very special properties. By doping these surface states with iron, the surface band structure can be explored and controlled.

A neutron-scattering study provides quantitative evidence for magnetically mediated superconductivity close to a quantum critical point in the heavy fermion superconductor CeCu₂Si₂.

Electron spins in semiconductor structures are quantum bits with good prospects, but the information stored in the spin states tends to degrade quickly owing to interactions with nuclei in the host material. A study of GaAs quantum dots now provides a fuller understanding of this memory loss and how it can be suppressed. Quantum-memory times exceeding 200 μs are demonstrated, two orders of magnitude longer than previously reported for this system.

Single-molecule techniques and femtosecond pulse shaping are now combined to investigate quantum coherence in biomolecules. The creation and manipulation of such coherence enables a basic single-qubit operation with terrylene diimide at room temperature.

Atoms trapped in optical lattices have been used successfully to study many-body phenomena. But the shape that bosonic ground-state wavefunctions can take is limited, compromising the usefulness of this approach. Such limitations, however, do not apply to excited states of bosons. An atomic superfluid that has now been realized in such a higher-energy band promises to provide insight into a wider range of many-body effects.

Quantum cascade lasers can operate at terahertz frequencies because they use intraband, rather than interband, transitions in semiconductor nanostructures. However, they seemed to have reached a ceiling in terms of maximum operating temperature. This trend has now been broken with the introduction of a new scheme for charge injection.