Volume 10 Issue 3, March 2014

Comparisons between classically simulated models and the actual performance of a 100-qubit D-Wave processor stimulate, but do not settle, the debate about how quantum annealing really works.

The Dzyaloshinskii–Moriya interaction — the mechanism behind weak ferromagnetism — has been difficult to probe experimentally. Now, significant progress is reported that has important implications for a wide range of magnetic phenomena.

A recent experiment shows that graphene nanoribbons can be grown to be perfect conductors where electrons travel long distances without coming across a single obstacle.

Iron pnictide superconductors often feature nematic, symmetry-breaking electronic states. These phenomena are now found to persist into the tetragonal phase of NaFeAs — a new piece of information that may help settle the fundamental origin of nematic electronic states.

Disks interacting via particular potentials self-organize into triangles that stabilize mosaics with 10-, 12-, 18- and 24-fold symmetry, as revealed by computer simulations. Discoveries of further novel quasicrystals may now be within reach.

The back-action of a weak measurement on the electron spin of a nitrogen–vacancy centre in diamond can be used to steer the associated nuclear spin towards a desired state.

Quantum measurements affect the state of the system, so they can be used both as probe and control knob. This idea is demonstrated in an experiment with nuclear spin qubits in diamond that are manipulated by measurements alone.

Quantum critical behaviour has been observed in many metallic systems that do not behave conventionally as Fermi liquids. High-magnetic-field experiments now reveal clear evidence for quantum criticality in an iron-based high-temperature superconductor.

The physics of one-dimensional many-body systems is rich but still insufficiently understood. An ultracold atom experiment investigates the behaviour of one-dimensional strongly correlated fermions with a tunable number of spin components.

Oxygen-mediated superexchange (or Dzyaloshinskii–Moriya) interactions result in weak ferromagnetism in oxides. A method based on the interference of synchrotron X-ray radiation is now shown to enable the determination of the sign of the Dzyaloshinskii–Moriya interaction in the prototypical weak ferromagnet iron borate.

To better understand the mechanisms of double ionization following the absorption of one photon, a combination of experimental techniques has been developed to probe the electron emission times in xenon on the attosecond timescale.

Bacteria often reside in fluids. Now, it is shown that hydrodynamic shear, which creates forces and torques on bacterial suspensions, stimulates the attachment of bacteria to surfaces and seriously hinders chemotaxis.

Quantum annealing is expected to solve certain optimization problems more efficiently, but there are still open questions regarding the functioning of devices such as D-Wave One. A numerical and experimental investigation of its performance shows evidence for quantum annealing with 108 qubits.

Superconductivity in iron pnictides seems to be related to the formation of electronic nematic phases that break the rotational symmetry of the crystal lattice. But the nematic phase in NaFeAs is now shown to persist at high temperatures owing to the presence of antiferroic fluctuations.

Graphene and topological-insulator surfaces are well known for their two-dimensional conic electronic dispersion relation. Now three-dimensional hyperconic dispersion is shown for electrons in a HgCdTe crystal—once again bridging solid-state physics and quantum electrodynamics.

Beware a sure thing.