Letters in 2010

The speed with which symmetry breaking transitions occur in the solid state makes them difficult to study in the time domain. State-of-the-art pump–probe measurements of the dynamics of charge-density waves in terbium telluride enable the evolution of the symmetry breaking charge-order transition of this system to be studied with unprecedented temporal resolution.

Monitoring the photocurrent generated as a laser scans across a graphene field-effect device subjected to low temperature and high magnetic fields enables the spatial distribution of Landau levels across a graphene sheet to be mapped. This in turn allows the relative contribution of bulk and edge states to the macroscopic electrical characteristics of these devices to be determined.

Although solar flares are the most energetic events that occur in our Solar System, very little is known about their contribution to the total energy the Earth receives from the Sun. The identification of a measurable signal from a moderate-sized solar flare in total solar irradiance data suggests their impact on the variability of the Sun’s output could be larger than expected.

Amplifying a signal usually also amplifies the noise. A quantum-state amplifier is now demonstrated that can actually decrease uncertainty about the state’s phase. Counterintuitively, the concept involves the addition of thermal noise.

A pure spin current has no net charge current and is therefore difficult to detect. A new technique that takes advantage of nonlinear optical effects can measure pure spin currents non-invasively, non-destructively and in real-time.

Micrometre-scale superconducting circuits are at present explored as the building blocks for scalable quantum information processors. In a system where two such qubits are coupled to a resonant cavity, tripartite interactions and controlled coherent dynamics have now been demonstrated. This platform should allow for a fuller exploration of multipartite quantum states and their deterministic preparation.

A new technique for controlling the quantum state of a superconducting qubit is now presented. Microwave pulses are applied in such a way that they excite only one of a pair of degenerate states. The concept enables construction of a controlled-NOT gate, a device important for quantum logic.

The electronic properties of metals are usually well described by Fermi-liquid theory. However, whether it still applies to very thin metal films has been unclear. Now, measurement of the lifetime of hot electrons in lead films just a few monolayers thick suggests that it does, and in turn provides a reliable means for determining the lifetime of excited carriers in bulk metals.

Pinching is a process most commonly associated with the break-up of liquid streams in air. Time-resolved three-dimensional X-ray imaging of a eutectic Al–Cu alloy reveals that interfacial-energy-driven bulk diffusion can drive similar processes in liquid–solid systems

The Jaynes–Cummings model describes the interaction between a two-level system and a small number of photons. It is now shown that the model breaks down in the regime of ultrastrong coupling between light and matter. The spectroscopic response of a superconducting artificial atom in a waveguide resonator indicates higher-order processes.

As a measure of disorder, entropy is a central concept of statistical mechanics. In practice, however, it is typically determined thermodynamically, that is, by measuring heat. However, in arrays of interacting submicrometre-sized magnetic islands—known as artificial spin ice—entropy can be determined directly by ‘counting’ the microstate of the system.

The Heisenberg uncertainty principle bounds the uncertainties about the outcomes of two incompatible measurements on a quantum particle. This bound, however, changes if a memory device is involved that stores quantum information. New work now extends the uncertainty principle to include the case of quantum memories, and should provide a guide for quantum information applications.

Bosons in an optical lattice are used to simulate the Bose–Hubbard model. If the lattice is disordered, a Bose glass is predicted to exist. Transport measurements in such a lattice provide evidence for a disorder-driven superfluid–insulator transition into a Bose-glass state.

Single nitrogen–vacancy centres in diamond are a prime candidate for implementing scalable quantum information processing at room temperature. Work so far has been focused on using the ground state of these defects, but an experimental study now suggests that the excited state is a promising route to fast gate operation.

Experimental data suggest that EtMe₃Sb[Pd(dmit)₂]₂, an organic system with a two-dimensional triangular lattice, undergoes a low-temperature phase transition that is not accompanied by classical antiferromagnetic ordering, hinting towards a hitherto unknown quantum state of matter.

Owing to incomplete data, it is difficult to establish tropical cyclone behaviour over long timescales. However, by considering the total released energy of individual cyclones, it is possible to establish changes of cyclone energy and their connection to climate change.

An ultracold gas of strongly interacting fermions exhibits a pseudogap phase in which pairs of fermions exist above the superfluid transition, but lack the phase coherence of a superfluid.

High-temperature copper oxide superconductors are usually doped with holes or electrons, not both. The discovery of a material that can be doped with both electrons and holes finally clarifies the region of low doping and the effect of the added dopants.

Phase transitions in water are normally classified as first or second order. But in confined quasi-one-dimensional films of water, simulations show that the solid–liquid transition can take place by means of a first-order transition or a continuous one without a distinction between solid and liquid.

Theory predicts that the conditions generated by acoustic cavitation of a liquid could be enough to drive thermonuclear fusion. But convincing experimental evidence of this is lacking. New results now suggest that the conditions achieved are comparable to those produced in laser-driven fusion experiments.