Articles in 2014

When superconducting discs are deposited on graphene they induce local superconducting islands. The phase coupling between the islands can be controlled by a gate. Quantum phase fluctuations kill the superconductivity and lead to a metallic state, however, at higher magnetic fields superconductivity can return.

An optomechanical system that converts microwaves to optical frequency light and vice versa is demonstrated. The technique achieves a conversion efficiency of approximately 10%. The results indicate that the device could work at the quantum level, up- and down-converting individual photons, if it were cooled to millikelvin temperatures. It could, therefore, form an integral part of quantum-processor networks.

Although the concept of a quasiparticle—a particle plus interactions—works very well for some problems, in other cases quasiparticles can be destroyed by quantum fluctuations. Alternative theoretical techniques for handling strong interactions are needed, such as those from string theory.

The transport and relaxation mechanisms in organic semiconductors are still insufficiently understood, but measurements now show that in these materials polarons carry pure spin currents over extended distances with long relaxation times, and uncover the role of spin-orbit coupling in this process.

Spin–orbit coupling in Bose gases is expected to lead to new phenomena, but the thermodynamic properties are not yet fully understood. An ultracold atom experiment using artificial spin–orbit coupling uncovers the finite-temperature phase diagram and a transition between a stripe-ordered and a magnetized phase.

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.

Biomembranes can transmit forces over cellular length scales. Now, however, their active role in generating stress is demonstrated. The adhesion and spreading of a liposome that has no active cytoskeletal machinery are shown to contract the substrate, exerting traction stresses that are comparable with those of living cells.

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.

A mechanism for coupling the electrons and vibrational motion of a suspended carbon nanotube is now demonstrated. Tailoring the coupling between specific electronic and phononic modes by controlling the position of quantum dots along the resonating tube enables spatial imaging of the mode shape.