Volume 10 Issue 2, February 2014

The latest generation of optical atomic clocks has reached such a degree of accuracy that questions about the need to redefine the second are raised. But even without such a redefinition, these breakthroughs will enable unprecedented precision tests of fundamental physics.

Experiments in microfluidics reveal long-range orientational correlations in the velocities of flowing droplets that can be rationalized in terms of an analytically solvable model.

The density of monopoles in spin ice can be enhanced by rapid cooling. After the creation of significant numbers of monopoles, magnetization measurements show that, much like charges in an electric field, monopoles can be driven by a magnetic field.

In the presence of light-induced spin–orbit coupling, ultracold atoms form pairs with a spin-triplet component. Creating these pairs is an important step towards realizing atomic superfluids with topological excitations.

The no-cloning theorem is challenged by super-replication, a process that takes a number of copies of a state and produces a quadratically larger number of exponentially close-to-perfect copies — the catch being the low odds of success.

Defects in the crystal lattice of silicon carbide prove to be a useful room-temperature source of non-classical light.

Chemical doping is a standard method of tuning electronic and structural properties of materials. Now, it has been shown that doping a pure superconductor can induce a percolative transition to magnetism.

Nematic order in the iron-based superconductors breaks the symmetry between the x and y directions in the Fe plane. Beyond this, however, there is little consensus on how nematic order arises and whether it has an effect on superconductivity. This Review discusses the current theoretical and experimental state of the field.

In open quantum systems the correlations between the system and its environment play an important role. A trapped-ion experiment demonstrates that these correlations can be detected without accessing or knowing anything about the environment or its interactions.

The creation of Feshbach molecules by exploiting engineered spin–orbit coupling in a spin-polarized Fermi gas advances the experimental study of topological superfluidity in ultracold gases.

Ultracold atoms could help in understanding the physics of strongly interacting many-body systems, but the creation of degenerate Bose gases at unitarity has been hampered by the losses. An experiment overcomes these problems and investigates the time evolution of a unitary Bose gas.

Chemical substitution often mimics the effects of applied pressure on a compound, and ‘doping’ is a standard way to reach a quantum critical point from a given phase. However, CeCoIn₅ is a natural quantum critical superconductor, and Cd-doping tunes the system away from criticality. Applied pressure reverses the effect of doping, but although superconductivity is restored, quantum criticality is not.

CeCoIn₅ is a d-wave heavy-fermion superconductor. By tuning the coupling between magnetic and superconducting order, a phase with inhomogeneous p-wave superconductivity can be detected, which coexists with d-wave superconductivity and spin-density-wave order.

Monolayer and few-layer materials present interesting spin and pseudospin states. A study of the coupling between spin, valley and layer degrees of freedom in bilayer WSe₂ reveals coherent superpositions of distinct valley configurations and suggests the possibility of electrical control of the spin states.

Magnetic monopoles can exist in frustrated magnetic systems known as spin ices. The study of these exotic objects is challenging, but a technique that uses the quench parameters to control the number of monopoles could help.

Ensembles of micrometre-sized water droplets in a laminar oil flow are ideal systems for studying non-equilibrium dynamics. In the case of two-dimensional confinement, the interactions between the droplets’ flow-induced dipole moments lead to long-range velocity correlations and four-fold angular symmetry—behaviour that can be understood from first-principle hydrodynamics calculations.

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.

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.

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.

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.

Out of sight, out of mind.