Articles in 2011

In the copper oxide superconductors, spin fluctuations might be involved in the electronic pairing mechanism. The case for such magnetically mediated superconductivity is now strengthened by the discovery of high-energy magnetic excitations that are not affected by chemical doping levels within several cuprates.

Where a superconductor has a node, or a zero, in the superconducting gap, low-energy excitations exist that are similar to those in normal metals and are thought to be unaffected by superconductivity. However, excitation of superconductors with a near infrared pulse reveals there is a link between these excitations and superconductivity.

The Prigogine–Defay ratio quantifies how many parameters are needed to fully characterize the glass-transition behaviour of a viscous liquid. For a single parameter, this ratio is unity, but it has never been clear whether any real liquid has such a value. A discovery of a connection between this ratio and the density scaling behaviour of silicone oil suggests it does.

A nitrogen impurity in diamond—where two of the carbon atoms are replaced by a nitrogen atom and a vacant lattice site—is seen as a valuable qubit. The spin of an electron localized to the nitrogen-vacancy centre is commonly used for processing. Researchers now show that this electron spin state can be transferred to the nitrogen nuclear spin, where it can be stored until needed.

Atomic and molecular gases generate extreme ultraviolet light when excited by pulses of intense laser light. This emission provides information about the inner workings of the molecules and even enables us to map electron orbitals. However, so far molecular orbital tomography has been restricted to simple molecules. A technique that can be applied to more complicated molecules is now unveiled.

In a Mott insulator, strong repulsive interactions suppress conductivity. Such behaviour has been demonstrated, individually, for both bosonic and fermionic atoms confined to optical lattices. Now, a dual Mott insulator of bosons and fermions has been realized, and interspecies interaction are found to markedly modify each Mott insulator.

Optical quantum memories—storage devices for the data encoded in light pulses—will be vital for buffering the flow of quantum information. Researchers now demonstrate such a device that can operate at room temperature. The quantum state is stored in a vapour of rubidium atoms and then recalled with a fidelity in excess of 98%.

Antihydrogen has been created, trapped and stored for 1,000 s. The improved holding time means that we now have access to the ground state of antimatter—long enough to test whether matter and antimatter obey the same physical laws.

Understanding how DNA bends and stretches provides insight into how the genetic information it contains is expressed. However, the role that the double-helical shape of DNA plays in determining its mechanical properties has not previously been investigated. Now, a model that incorporates DNA’s famous shape provides a better understanding of how the molecule reacts to large forces.

The combination of bulk momentum-space and local real-space probes shows that superconductivity and antiferromagnetism in an electron-doped copper oxide superconductor coexist and compete on a nanometre scale, with electronic spin excitations that are probably involved in the superconducting pairing mechanism.

A technique to study the noise in quantum systems has been devised by using spectral filters in reverse. So-called dynamical-decoupling pulse sequences, previously used to remove noise, now quantify how a superconducting qubit interacts with its noisy environment.

NMR is typically carried out in strong magnetic fields, but recent technological developments have enabled the development of different methods for creating and detecting nuclear magnetization that do not depend on the use of strong magnets. A study that combines such methods demonstrates now that high-resolution NMR spectra with chemically relevant information can be obtained at zero magnetic field.

A demonstration of attosecond control of the motion and directed emission of electrons from individual silica nanoparticles using few-cycle laser fields opens new possibilities to manipulate electronic processes in nanoscale systems.

Its tunable energy bandgap makes bilayer graphene interesting both from a theoretical perspective and with a view to applications. But exactly how the bandgap is formed is still unclear. A scanning tunnelling spectroscopy study now finds that the microscopic picture of the gap is fundamentally different from what is expected from macroscopic measurements and currently developed theories.

Exciton-polariton fluids—which are composed of composite light–matter bosons—provide an experimental means for studying quantum fluids that are intrinsically out of equilibrium. These authors demonstrate the nucleation and dynamics of vortex–anti-vortex pairs in the flow of exciton-polaritons passing around an obstacle, and establish these systems as a platform for studying quantum turbulence.

Quantum strategies can help to make parameter-estimation schemes more precise, but for noisy processes it is typically not known how large that improvement may be. Here, a universal quantum bound is derived for the error in the estimation of parameters that characterize dynamical processes.

That Brownian particles in a liquid move diffusively at long times but ballistically at very short times has been understood for more than a century. However, the full details of the transition between these regimes are yet to be explored. Now, the transition from ballistic to diffusive Brownian motion has been measured for the first time.

An ‘attoclock’ that measures the relative release time of electrons during double ionization is now presented. The technique enables investigation of the subtle differences between sequential and non-sequential ionization when elliptically polarized light is used to excite two electrons from argon atoms.

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.

Extensive datasets such as those capturing the movement of mobile-phone users have provided us with a new basis for modelling human mobility, a process that has been shown to be highly predictable. This study now shows how recurrent patterns in how we move influence contagion processes, such as the spatial spread of infectious diseases.