Articles in 2013

Double quantum dots are proving themselves to be an excellent test bed for many-body physics. These artificial atoms now demonstrate a phenomenon in which the capacitive coupling between them causes the spin and charge degrees of freedom of the electrons in the system to become entangled—the so-called SU(4) Kondo effect.

Assemblies of colloidal particles provide a micrometre-scale analogue of atomic and molecular liquids and solids. Now, real-time visualization of the liquid-solid transition in systems of spherical colloids reveals complex pathways involving precursors of hexagonal close-packed, body-centred cubic and face-centred cubic symmetry.

Defects in silicon carbide can produce continuous-wave microwaves at room temperature. Spectroscopic analysis indicates a photoinduced inversion of the population in the spin ground states, which makes the defects a potential route to stimulated amplification of microwave radiation.

It is shown that for thermodynamics and statistical physics to be internally consistent, Gibbs’ original—rather than Boltzmann’s widely used—definition of entropy needs to be adopted. Consequently, negative absolute temperatures are strictly forbidden, and cold-atom gases are unlikely to be laboratory analogues to dark energy.

The mathematical connection between isostatic lattices—which are relevant for granular matter, glasses and other ‘soft’ systems—and topological quantum matter is as deep as it is unexpected.

A room-temperature motion sensor with record sensitivity is created using a levitating silica nanoparticle. Feedback cooling to reduce the noise arising from Brownian motion enables a detector that is perhaps even sensitive enough to detect non-Newtonian gravity-like forces.

Inelastic X-ray scattering studies of YBa₂Cu₃O_6.6 reveal strong electron-phonon coupling and an inhomogeneous state made up of charge-density-wave nanodomains, which may explain some anomalous properties of the pseudogap state.

Ferroelectric domain switching on the surface of a lithium niobate thin film can be induced by the tip of a scanning probe microscope, and gives rise to both regular and chaotic spatiotemporal patterns. Moreover, the long-range interactions that govern these phenomena can be tuned by varying temperature, humidity, domain spacing and tip bias.

A high-confinement plasma that is potentially useful for controlled fusion has now been sustained for over 30 s. The Experimental Advanced Superconducting Tokamak in Hefei, China, achieved this record pulse length by first confining the plasma using lithium-treated vessel walls, and then maintaining it with a so-called lower hybrid current drive.

An electron and a hole trapped in the same quantum dot couple together to form an exciton. Conventionally the hole involved is a heavy hole. Light-hole excitons are now observed by applying elastic stress to initially unstrained gallium arsenide-based dots. The quasiparticles are identified by their optical emission signature, and could be used in future quantum technologies.

In the band theory of solids, the topological properties of Bloch bands are characterized by geometric phases. For cold atoms moving in a one-dimensional optical potential the geometric phase can be measured directly using Bloch oscillations and Ramsey interferometry.

A combination of measurements from the Solar Dynamics Observatory and radiospectroscopy data from the Nançay Radioheliograph now details the mechanism that connects coronal mass ejections from the sun and the acceleration of particles to relativistic speeds. A spatial and temporal correlation between a coronal ‘bright front’ and radio emissions associated with electron acceleration demonstrates the fundamental relationship between the two.

Superparamagnetism (preferential alignment of spins along an easy axis) is a useful effect for spintronic applications as it prevents spin reversal. It is now shown that high-spin quantum dots can become magnetically anisotropic when coupled to nearby ferromagnets—‘artificial’ superparamagnets.

Can Alice verify the result of a quantum computation that she has delegated to Bob without using a quantum computer? Now she can. A protocol for testing a quantum computer using minimum quantum resources has been proposed and demonstrated.

Emerging sensing and quantum-information technologies based on nitrogen–vacancy centres in diamond require a better understanding of the relaxation mechanisms. A two-dimensional spectroscopy study provides information about the effects of the vibrational bath on the electronic dynamics.

Bulk vanadium dioxide undergoes a metal–insulator transition near room temperature. It is now shown that by putting a thin layer of vanadium dioxide on a buffer, and varying the buffer’s thickness, the orbital occupancy in the metallic state and the transition temperature can be tuned.

A quantum critical point associated with a carbon nanotube quantum dot that is in contact with dissipative leads exhibits striking non-Fermi-liquid properties and anomalous scaling. The dissipative environment enables the comparison of the system under thermal- and non-equilibrium conditions.

If correlations decay exponentially in a one-dimensional quantum many-body system, then entanglement satisfies an area law. The intuitive explanation for this turns out to be wrong, but the statement is nevertheless true, as demonstrated by a proof based on quantum information theory.

The Kibble–Zurek mechanism describes the spontaneous formation of defects in systems that are undergoing a second-order phase transition at a finite rate. Familiar to cosmologists and condensed matter physicists, this mechanism is now found to be responsible for the spontaneous creation of solitons in a Bose–Einstein condensate.

Models for the topology or dynamics of various networks abound, but until now, there has been no single universal framework for complex networks that can separate factors contributing to the topology and dynamics of networks across biological and social systems.