Volume 7 Issue 6, June 2011

Spectroscopic techniques typically probe the interaction between matter and electromagnetic fields. An experiment now demonstrates that transitions between quantum states of neutrons can be brought about by mechanically vibrating a mirror, an approach that may lead to sensitive tests of gravity laws.

Evidence is growing that quantum coherence plays a role in photosynthesis. Better understanding of this process might help us design more efficient solar cells to harness the Sun's energy.

'Standard' qubits have been implemented in diverse physical systems. Now, so-called topological qubits are coming into the limelight, and could potentially be used for decoherence-free quantum computing. Coupling these two types of qubit might enable devices that exploit the virtues of both.

Direct measurements of the energy dissipated by quantum turbulence clearly demonstrate that the scaling of the long-time decay of the energy dissipation in the quasiclassical regime of turbulence differs from that in the ultraquantum regime.

Single colour centres in diamond have already proved their merit for sensing magnetic fields with high sensitivity and spatial resolution. Now they have been shown to be effective atomic-scale probes of electric fields, too.

Superconducting phase fluctuations are often associated with the pseudogap phase of the copper-oxide superconductors. However, the same fluctuations exist in the overdoped part of the phase diagram where the pseudogap is absent, suggesting that phase fluctuations are independent of the pseudogap

Point defects in diamond known as nitrogen-vacancy centres have been shown to be sensitive to minute magnetic fields, even at room temperature. A demonstration that the spin associated with these defect centres is also sensitive to electric fields holds out the prospect of a sensor that can resolve, under ambient conditions, single spins and single elementary charges at the nanoscale.

High-harmonic spectroscopy probes atomic structure by looking at the short-wavelength emission excited from atoms by ultrafast pulses of laser light. It is now shown that this technique can even detect signatures of electron–electron interactions.

Spectroscopic techniques are mostly used to study the interaction between matter and electromagnetic fields. Here, an experiment that probes the transitions between quantum states of neutrons in the Earth’s gravitational field demonstrates an exotic variant of spectroscopy, and one that might lead to sensitive fundamental tests of gravity laws.

It is difficult to measure the turbulent energy in a classical system as the turbulence contributes only a small kinetic energy compared with the enthalpy of the system. A quantum system, however, such as liquid helium at absolute zero, has zero enthalpy. Added vorticity therefore accounts for the total energy, thus allowing the turbulent energy to be measured directly

Stretching and folding are distinct processes that govern turbulent mixing, but distinguishing them in experiments has proved difficult. By adapting tools more commonly used to study glasses, it is now possible to determine their individual contributions in two-dimensional flows.

Many properties of physical systems are known to depend on their dimension. But for complex networks—which serve to model a wide range of physical, technological and social systems—the concept of dimension has received relatively little attention so far. This study shows how the dimension of a broad class of networks can be ascertained, and demonstrates that it determines the basic properties of the networks.

As the pnictide superconductors have metallic ground states, the Heisenberg model has not been successful in describing the magnetic behaviour. But the addition of a biquadratic interaction term to the usual Heisenberg Hamiltonian leads to a description of many experimental observations.

The ability to switch a semiconductor into a topological insulator would produce topological states on demand. Applying a time-dependent field to well-studied semiconductor quantum wells may lead to this kind of control.

One of the fundamental questions of nanoscale spin-transport is how a spin-polarized current interacts with a ferromagnet under finite bias. So far, experimental results have remained inconclusive, but a novel technique allows direct and quantitative measurements of the spin-transfer torque in magnetic tunnel junctions and should provide a basis for understanding and modelling the phenomenon.

The investigation of how chemical reactions depend on molecular orientation has a long history. In particular, the spatial anisotropy of the dipole–dipole interaction between polar molecules leads to a dependence of stereodynamics of collisions on long-range interactions. A study with ultracold molecules, where all internal and external states of the molecules can be controlled, now extends such studies into the quantum regime.

Permeable membranes play a vital role in many biological processes. Simulations of Brownian motion now show that the spatially correlated disorder of these membranes unexpectedly modifies diffusion rates.