Volume 6 Issue 10, October 2010

The finding that a network of 'leaky' neurons can sustain activity-burst avalanches links the science of criticality to that of realistic brain models.

It is possible to noiselessly amplify a quantum state by first deliberately increasing its noise. This paradoxical result may have important applications in quantum communication and metrology.

Humans tend to explore unknown locations, but preferentially return to familiar places. The interplay between these two basic behaviours accounts for many of the scaling relations observed in human-mobility patterns.

Thermal noise destroys the fragile correlations that characterize many-body systems at a quantum critical point. Theoretical work now shows that another generic form of noise acts differently: flicker noise may alter some properties of a quantum phase transition, but it can preserve the quantum critical state.

Cells are the building blocks of life. Ideas traditionally applied to physical problems are now helping to unravel their complex mysteries.

Cell biophysics sheds some new light on cancer by approaching this complex problem from a materials science perspective.

Viruses are protected by a protein shell known as a capsid. The mechanical properties of capsids have been the focus of intense experimental and theoretical investigation with the hope that a better understanding will open the door to new medical treatments and applications in biotechnology.

Is the brain on the edge of criticality? Understanding the inner workings of the brain is a task made difficult by the number of elements involved: a hundred billion neurons and a hundred trillion synapses. Viewing the brain in terms of collective dynamics is one approach now yielding some insight.

A protein’s shape is crucial for fulfilling its function within a cell. This Review discusses how molecular dynamics simulations have given us insight into the processes that turn a linear chain of amino acids into a unique three-dimensional protein.

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.

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.

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.

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.

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.

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 Peregrine soliton — a wave localized in both space and time — is now observed experimentally for the first time by using femtosecond pulses in an optical fibre. The results give some insight into freak waves that can appear out of nowhere before simply disappearing.

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

Self-organized criticality has been observed in a number of complex systems, including neuronal networks. Another property of cortical networks is that a high proportion of neurons collectively alternate between high activity (so-called up states), and quiescence (down states). Theoretical work now shows these two phenomena are intimately related.

Quantum critical points in many-body systems are characterized by the appearance of long-range entanglement. These subtle quantum correlations are known to be extremely fragile with respect to thermal noise. But theoretical work now shows that, unexpectedly, another classical disturbance, the ubiquitous 1/f noise, does preserve the critical correlations.

Real-space mapping of the quantum Hall state at the Dirac point in epitaxial graphene reveals unexpected localized lifting of the degeneracy of this level. This could be the result of moiré interference caused by the twisting of the top layer with respect to underlying layers, suggesting possible new ways to understand and control the unusual properties of graphene.

Extensive data sets of trajectories of mobile-phone users provide a new basis for modelling human mobility. Random-walk models can capture some aspects, but go only so far. Now, two governing principles for human mobility are proposed, exploration and preferential return, paving the way to a more appropriate microscopic model for individual human motion.

Looking at cells from a mechanistic perspective can provide insight into their behaviour and function that is not available through more empirical approaches. Numerical techniques and material-characterization experiments common in many physics laboratories are now proving to be useful tools in biology too.