Research articles

The Landau–Zener model of a two-state system is a standard method for studying quantum dynamics. This textbook example of single-particle dynamics has now been generalized to a many-body system represented by two coupled ultracold Bose liquids.

Laser light can trap and manipulate small particles. Scientists now show that femtosecond near-infrared laser pulses can split a single trap into two. The effect is a result of third-order optical nonlinearities that arise once the laser power crosses a certain threshold, and the direction of the split is determined by the light’s polarization.

Magnetic reconnection governs many astrophysical phenomena, but its details are poorly understood. The extreme magnetic fields generated by the interaction of a high-intensity laser with a plasma enables the study of magnetic reconnection processes similar to those that occur in solar flares.

Quantitative measurements that establish the existence and evolution of quasiparticles across the whole phase diagram of a cuprate superconductor help to distinguish the many theoretical models for high-temperature superconductivity.

Raman amplification has been proposed as a means to generate high-power laser pulses without the bulky and expensive components of conventional lasers, but with limited success. Large-scale three-dimensional simulations enable researchers to identify conditions under which these limitations might be overcome.

The ability to generate entangled photon pairs from a quantum dot critically depends on the size of the fine-structure splitting of its exciton states. A demonstration of the ability to tune this splitting with an electric field represents a promising step in the use of quantum dots to generate entangled photon pairs on demand.

A study of Mn-doped InAs quantum wells reveals unexpected metastable behaviour of magnetotransport phenomena at sub-kelvin temperatures, in structures that show at the same time the quantum Hall effect in high magnetic fields. These findings bridge the physics of two-dimensional carrier systems with phenomena specific to magnetically doped semiconductors.

A major goal in the fields of ultracold quantum gases and quantum simulations is measuring the phase diagram of strongly interacting many-body systems. This has now been achieved in an optical-lattice-based quantum simulator. The simulation is validated through an ab initio comparison with large-scale numerical quantum Monte Carlo simulations.

The energy potentials created by laser light can trap atoms. An analogous effect that traps electrons in solid-state systems is now proposed. The electron traps are created in quantum wells and wires in the presence of quasiparticles composed of two electrons and a hole. The idea could lead to advances in ultrafast optical and new optoelectronic devices.

A noisy environment is used to study the dynamics of a four-trapped-ion entangled state. The study shows that entanglement properties such as distillability and separability can be altered by controlling the degree of dephasing. The results provide an important insight into the nature of multiparticle entanglement.

Loading only single atoms into an optical trap with an efficiency in excess of 80% has now been achieved by manipulating the collisions between pairs of atoms. Such a process has previously been limited to about 50% efficiency. The technique will aid the development of neutral-atom-based quantum logic gates.

Atomic transitions afford a convenient way of storing quantum bits. However, there are few ground-state transitions suitable for use with light at telecommunication wavelengths. Now, researchers show that ensembles of cold rubidium atoms not only make good quantum memories, but can also noiselessly convert the emitted photons into and out of the telecoms band.

The experimental demonstration of heat currents driving the injection of spins from a ferromagnetic into a non-magnetic metal establishes a new source of pure spin currents. The approach might provide an alternative mechanism for switching processes in memory devices and for other ‘spintronics’ applications.

When doped with copper, the topological insulator Bi₂Se₃ becomes superconducting. But for new physics and applications the search is not for just any superconductor; the material must retain its topological character. And indeed that is the case with doped Bi₂Se₃.

Erwin Schrödinger introduced in 1935 the concept of ‘steering’, which generalizes the famed Einstein–Podolsky–Rosen paradox. Steering sits in between quantum entanglement and non-locality — that is, entanglement is necessary for steering, but steering can be achieved, as has now been demonstrated experimentally, with states that cannot violate a Bell inequality (and therefore non-locality).

Diffraction conventionally limits the length scale on which spins can be optically probed. A new technique that uses doughnut-shaped beams of light to select just one nitrogen-vacancy centre, by suppressing the fluorescence from those around it, enables single-spin detection, imaging and manipulation with nanoscale resolution.

Single crystals of a two-dimensional quantum spin system with geometric frustration lead to the observation of a ‘pinwheel’ valence-bond ground state. In this case, the distortion of the ideal kagome lattice structure helps to stabilize the quantum spin state.

Introducing a phase shift between diffracted and undiffracted light from a sample is one of the oldest techniques for generating phase contrast in optical microscopy. A similar approach should help improve the contrast and clarity of images collected by scanning X-ray microscopy.

Extensive data sets of trajectories of mobile-phone users provide a new basis for modelling human mobility. Random-walk models can capture some aspects, but go only so far. Now, two governing principles for human mobility are proposed, exploration and preferential return, paving the way to a more appropriate microscopic model for individual human motion.

In one-dimensional systems, phase transitions at finite temperature are deemed impossible, because long-range correlations are destroyed by thermal fluctuations. Theoretical work now shows that, nonetheless, a phase transition at finite temperature can occur in a one-dimensional gas of weakly interacting bosons in a random environment