Volume 7 Issue 10, October 2011

A strictly one-dimensional electron liquid or 'Luttinger liquid' may seem a purely theoretical construct. But measurements of the electronic structure of strings of gold atoms self-aligned on a germanium surface suggest this mythic state of matter is real, offering new possibilities to investigate and ultimately control its properties and behaviour.

Quantum states of light could be a better probe for materials than classical states, but they are hard to generate in the laboratory. A scheme that combines large amounts of data with sophisticated theoretical analysis gets around this limitation.

A demonstration of the ability to produce arbitrary-shaped electron bunches from an ultracold gas represents an important step towards studying ultrafast molecular processes in laboratories around the world.

Electrons at an interface between two insulating oxides are now shown to exhibit ferromagnetism — a collective electronic state not seen in the bulk of either individual oxide.

For an important class of liquids, relaxation dynamics are constrained by a surprisingly simple scaling relationship between density and temperature. It seems that thermodynamics holds the key to pinning down the exponent.

Heisenberg’s uncertainty principle limits the precision with which we can measure two complementary properties of a quantum system. Entanglement, it has previously been proposed, can relax these constraints. This idea is now demonstrated experimentally with the aid of polarization-entangled photons.

The uncertainty principle tells us that two associated properties of a particle cannot be simultaneously known with infinite precision. However, if the particle is entangled with a quantum memory, the uncertainty of a measurement is reduced. This concept is now observed experimentally.

Lanthanum aluminate and strontium titanate are insulators, but when you bring them together, the interface between them becomes a two-dimensional superconductor. Even more surprising, magnetometry and transport measurements show that this superconducting state coexists with magnetic order.

When the insulators lanthanum aluminate and strontium titanate are brought together, the interface between them forms a two-dimensional superconductor. Moreover, magnetic imaging of this interface shows that superconductivity and ferromagnetism coexist in separated nanoscale domains.

Spin liquids are states of matter that reside outside the regime where the Landau paradigm for classifying phases can be applied. This makes them interesting, but also hard to find, as no conventional order parameters exist. The authors demonstrate that topologically ordered spin-liquid phases can be identified by numerically evaluating a measure known as topological entanglement entropy.

The Tomonaga–Luttinger liquid model is the leading candidate for describing one-dimensional metallic conductors at low temperature. Yet, experimental evidence that it is valid is sketchy. Scanning tunnelling and photoemission spectra suggest that it does, in fact, describe the behaviour of chains of gold atoms self-assembled on the surface of germanium.

Pump–probe measurements are now an essential tool for investigating ultrafast dynamics in atoms and molecules. A lack of sources producing high-intensity attosecond pulses of extreme-ultraviolet (EUV) light has, however, hindered progress. Now, a technique that induces nonlinear processes with EUV light is demonstrated that could circumvent this problem.

The potential to generate pulsed electron beams with charge distributions tailored in all three dimensions could revolutionize high-speed electron diffraction. A demonstration of a highly coherent pulse electron beam that can be arbitrarily tailored in two dimensions is a step towards this goal.

A nitrogen impurity in diamond—where two of the carbon atoms are replaced by a nitrogen atom and a vacant lattice site—is seen as a valuable qubit. The spin of an electron localized to the nitrogen-vacancy centre is commonly used for processing. Researchers now show that this electron spin state can be transferred to the nitrogen nuclear spin, where it can be stored until needed.

Optical quantum memories—storage devices for the data encoded in light pulses—will be vital for buffering the flow of quantum information. Researchers now demonstrate such a device that can operate at room temperature. The quantum state is stored in a vapour of rubidium atoms and then recalled with a fidelity in excess of 98%.

Experiments that exploit non-classical properties of light promise to provide unique information about many-body systems. The limited availability of non-classical light sources, however, makes their implementation challenging. A method to calculate the quantum-optical response of a material from signals measured by using coherent-light excitation might provide an alternative route.

Where a superconductor has a node, or a zero, in the superconducting gap, low-energy excitations exist that are similar to those in normal metals and are thought to be unaffected by superconductivity. However, excitation of superconductors with a near infrared pulse reveals there is a link between these excitations and superconductivity.

Mechanical deformations in graphene have been shown to be associated with ‘fictitious’ magnetic fields. Theoretical work now suggests that these fields can give rise to an analogue of the Aharonov–Bohm effect, a phenomenon that might be used to sensitively detect small deformations of the graphene sheet.

The Prigogine–Defay ratio quantifies how many parameters are needed to fully characterize the glass-transition behaviour of a viscous liquid. For a single parameter, this ratio is unity, but it has never been clear whether any real liquid has such a value. A discovery of a connection between this ratio and the density scaling behaviour of silicone oil suggests it does.

Atomic and molecular gases generate extreme ultraviolet light when excited by pulses of intense laser light. This emission provides information about the inner workings of the molecules and even enables us to map electron orbitals. However, so far molecular orbital tomography has been restricted to simple molecules. A technique that can be applied to more complicated molecules is now unveiled.