Articles in 2013

It has been suggested that plasmonic nanostructures could boost nonlinear optical processes in atoms. However, an incomplete understanding of the complex physics in such systems has hampered attempts to harness this idea in applications. An in-depth study now shows that phenomena such as high-harmonic generation might in fact be limited by the tiny volumes involved at the nanoscale.

Active materials, such as motile cells and self-propelled colloids, exhibit glassy effects, but little is known about the glass transition far from equilibrium. A study of model glasses subject to non-thermal driving and dissipation reveals signatures of dynamic arrest that can be understood in terms of an effective equilibrium description.

Linking two smoke rings or tying a single ring into a knot is no easy feat. Now, however, such topological vortices are created in water using 3D-printed hydrofoils. High-speed imaging shows how the linked rings spontaneously separate, and the knots are able to free themselves. Similar fluid dynamics may also be relevant in plasmas, quantum fluids and optics.

The efficiency of carrier–carrier scattering in graphene is now experimentally demonstrated. The dominance of this mechanism over phonon-related scattering means that a single high-energy photon could create two or more electron–hole pairs in graphene; an effect useful for optoelectronic applications.

Understanding the propagation of spin excitations is a difficult problem in quantum magnetism. Using site-resolved imaging in a one-dimensional atomic gas, it is possible to track the dynamics of a moving spin impurity through the Mott-insulator and superfluid regimes.

Understanding the origin of spin filtering in metal/organic interfaces is important for the control of spin injection in organic semiconductors. A time-resolved photoemission experiment shows that spin filtering can be explained by the trapping of electrons in spin-dependent potentials at the interface.

High-harmonic spectroscopy provides attosecond-scale information about optical processes in molecules. Present techniques, however, cannot simultaneously measure the phase as a function of molecular angle and photon frequency. An approach that retrieves both the amplitude and the phase of high-harmonic emission is now demonstrated, and could enable a full reconstruction of the molecular wavefunction.

Power-grid networks must be synchronized in order to function. A condition for the stability of the synchronous state enables identification of network parameters that enhance spontaneous synchronization—heralding the possibility of smart grids that operate optimally in real-world systems.

A megaelectronvolt beam of atoms is now generated by ionizing argon clusters, and then neutralizing the ions using Rydberg atoms. The compact system demonstrates a high neutral yield, and could find an important application as a sensitive probe of matter.

Controllable quantum systems can be used to emulate intractable quantum many-body problems, but such simulators remain an experimental challenge. Nuclear spins on a diamond surface promise an improved large-scale quantum simulator operating at room temperature.

A nanomechanical oscillator coupled to a superconducting waveguide provides all-microwave field-controlled tunable slowing and advancing of microwave signals, with millisecond distortion-free delay and negligible losses.

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.

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.