Volume 9 Issue 2, February 2013

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Spin coherence of valence holes in semiconductor quantum-dots is governed by interactions with the nuclear spins of the dot lattice. Experiments and theory have revealed an important new ingredient that determines the strength and sign of this coupling.

In superconductors spin and charge can be completely decoupled leading to unusual transport phenomena, such as nearly chargeless spin flow.

Superfluid ultracold gases in designer potentials are analogous to superconducting electronic circuits. The study of these systems refines our understanding of flow and dissipation in quantum fluids, and has applications for inertial sensing and metrology.

Techniques for understanding how a system responds to an infinitesimal perturbation are well developed — but what happens when the kick gets stronger? Insight into the topology of phase space may now provide the answer.

The elusive effects of quantum gravity could be betrayed by subtle deviations from standard quantum mechanics. An experiment using the gravitational wave bar detector AURIGA explores the limits of quantum gravity-induced modifications in the ground state of a mechanical oscillator cooled to the sub-millikelvin regime.

Quantum dots are a promising host for spin-based qubits. Whereas nuclear-field fluctuations adversely affect electron-spin coherence, the smaller hyperfine interaction between holes and nuclei makes holes a promising alternative. A sensitive measurement of the hyperfine constant of the holes in different quantum-dot material systems now demonstrates how this interaction can be tuned and perhaps further reduced.

A thermodynamic probe of the recently discovered charge-density-wave order in YBa₂Cu₃O_y reveals a biaxial modulation in magnetic fields up to 40 T.

Injection of spin-polarized electrons into a superconductor leads to both spin and charge imbalance. If charge relaxation occurs faster than spin relaxation, it is possible to observe excess spin at almost no extra charge.

Linear-stability measures for assessing the state of a dynamical system are inherently local, and thus insufficient to quantify stability against substantial perturbations. The volume of a state’s basin of attraction offers a powerful alternative—and points towards a plausible explanation for regularity in real-world networks.

The Efimov effect is a universal phenomenon displaying an infinite tower of three-body bound states. Recently it was observed in an ultracold atomic gas, and now Efimov physics has been predicted to exist in a quantum magnet.

Topological insulators are now shown to be protected not only by time-reversal symmetry, but also by crystal lattice symmetry. By accounting for the crystalline symmetries, additional topological insulators can be predicted.

A time-dependent study of the effective temperature of carriers in impurity-free graphene now indicates that a disorder-assisted mechanism is responsible for cooling hot electrons. Observation of this so-called supercollision contradicts the idea that electron–phonon interactions dominate cooling.

Charge transport is usually limited by collisions between the carriers, impurities and/or phonons. Collisions involving three bodies are generally much rarer. A study now reveals, however, that such supercollisions can play an important role in the properties of graphene.

Photosynthesis is remarkably efficient. The transport of optically generated excitons from absorbing pigments, through protein complexes, to reaction centres is nearly perfect. Simulations now uncover the microscopic mechanism that drives this coherent behaviour: interactions between the excitons and the vibrational modes of the pigment-protein complex.