Research articles

Rydberg molecules—which involve atoms in highly excited electronic states and can be as large as 100 nanometres—have been created recently in cold gases of rubidium atoms. New work demonstrates that the inter-atomic interactions in these long-range molecules can be manipulated coherently, enabling controlled ‘making and breaking’ of the bond using laser light.

Graphene has a random edge structure. According to theory, this dirty and random edge affects the topological nature of bilayer graphene, which accounts for measurement discrepancies across different experimental probes.

For an ideal topological insulator, the metallic surface states should be easy to measure using transport techniques; however, the bulk is not completely insulating. Improving the ‘leaky’ bulk state proves crucial for measuring the surface Dirac fermions, including correlation effects.

Networks of atom–cavity systems necessarily require that single atoms sit near dielectric interfaces. Real-time monitoring of caesium atoms just 100 nm from the surface of a micro-toroid resonator now demonstrates that the Casimir effect plays an important role in these systems.

Although carbon nanotubes are not superconductors they can carry supercurrents injected from superconducting contacts. Analysis of the tunnelling spectra of a nanotube connecting two superconductors reveals the detailed electronic structure of discrete entangled electron–hole states that carry the resulting supercurrent.

Feedback mechanisms such as the ‘demon’ in Maxwell’s well-known thought experiment can, in principle, enable the transformation of information into energy, without violating the second law of thermodynamics. Such information-to-energy conversion by feedback control has now been demonstrated experimentally.

Quantum information is often thought of in terms of manipulating discrete qubits. But continuous variables can also carry data. A method for storing continuous-variable states of light for up to a millisecond in room-temperature memories is now demonstrated.

A three-dimensional periodic structure focuses acoustic waves to a spot size that is one fiftieth of the wavelength—beating the classical diffraction limit by a long way. The device could lead to improved resolution for ultrasound imaging.

A dark exciton is an electron–hole pair with a very long radiative recombination time. Whereas their ’bright’ counterparts are studied in depth, dark states in quantum dots are often regarded as a nuisance. Now, a technique has been found for optically accessing dark excitons, which might make them more useful than first thought.

The rotation of polarized light in certain materials when subject to a magnetic field is known as the Faraday effect. Remarkably, just one atomic layer of graphene exhibits Faraday rotations that would only be measurable in other materials many hundreds of micrometres thick.

By varying the voltage on an isolated gate electrode beneath a graphene sheet, the ionization state of cobalt atoms on its surface can be controlled. This enables the electronic structure of individual ionized atoms, and the resulting cloud of screening electrons that form around them, to be obtained with a scanning tunnelling microscope.

The complex wrinkling patterns produced when a sheet or membrane is compressed are often difficult to predict. Observations of unexpected spatial period-doubling bifurcation instability in the wrinkling of a rigid membrane attached to a soft substrate can be described within a framework similar to that used for the parametric resonance of nonlinear oscillators.

In magnetic nanostructures, the core of a vortex points either up or down, and the polarity can be reversed by alternating-field pulses. An experiment now demonstrates deterministic and coherent control of vortex-core polarity using sequences of resonant microwave pulses and highlights routes to optimizing the technique, which might find application in magnetic-storage devices.

The absorption of one photon of an entangled pair by a lone trapped atom is identified by a correlation between the atomic absorption process and the detection of the second photon.

Betratron oscillations of electrons driven through a plasma by a high-intensity laser generate coherent X-rays. A new study demonstrates the intensity of these X-rays can be as bright as that generated by conventional third-generation synchrotrons, in a device a fraction of the size and cost.

Laser beams travelling side-by-side through a medium usually only interact if they’re within a beam-diameter apart. An observation of the attraction and coalescence of high-power beams separated by several beam diameters in a plasma has implications for the development of laser-driven fusion.

Tunnelling measurements reveal the emergence of a thickness-dependent in-built potential across LaAlO₃ thin films grown on SrTiO₃ substrates. As well as being useful for developing novel LaAlO₃/SrTiO₃ devices, these observations help explain the origin of the two-dimensional electron gas that is known to arise at the interface between these two insulators.

One-way quantum computing requires an entangled multiqubit system. So-called cluster states have been proposed to provide this resource, but they are difficult to generate. An alternative that uses the ground state of a one-dimensional chain of spins is now experimentally realized and used to construct a quantum logic gate.

A study of the electronic structure of molecular wires as a function of their length reveals strong coupling between electrons and molecular vibrations. The mechanism provides a means to coherently couple electronic levels by nuclear motion, and possibly to mechanically control electron transport in molecular electronics.

An array of nanomagnets in a kagome lattice structure should support the creation and separation of oppositely charged monopoles, which are connected by Dirac strings of flipped dipoles. And indeed, such monopoles and their Dirac strings can be observed at room temperature.