Articles in 2012

In 2000, Asher Peres put forward the paradoxical idea that entanglement could be produced after the entangled particles have been measured, even if they no longer exist. Researchers now experimentally demonstrate this idea using four photons.

Spin transfer torque—the transfer of angular momentum from a spin-polarized current to a ferromagnet’s magnetization—has already found commercial application in memory devices, but the underlying physics is still not fully understood. Researchers now demonstrate the crucial role played by the polarization of the laser light that generates the current; a subtle effect only evident when isolated from other influences such as heating.

A demonstration of the ability to coherently control the collective attosecond dynamics of relativistic electrons driven through a plasma by an intense laser represents an important step in the development of techniques to manipulate and study extreme states of matter.

It is well known that organisms profit from adapting to their environment. A study of stochastic adaptation dynamics shows that this comes at the expense of adaptive speed and accuracy—providing a framework for understanding adaptation in noisy biological systems.

Commutation relations define the limit to which two complementary properties can be simultaneously known—Heisenberg’s uncertainty principle. Yet it is thought that these canonical relations might be different in the quantum gravity regime. Researchers now show how quantum-optics experiments might provide a direct route for studying these effects.

The magnetic character of the cuprates is suspected by many to be involved in the emergence of unconventional superconductivity. The discovery of a second distinct magnetic excitation in HgBa₂CuO₄ supports a multiband picture of the magnetic structure of these materials.

Small-world topologies characterize many natural and human-built networks. Yet, how such networks organize their link weights is not fully understood. These authors report an organization scheme that captures important features of real-world systems, and identify learning rules that allow evolving networks to obtain such weight organizations based on their history.

An approach to first-principles simulations that incorporates dynamically screened Coulomb interactions between iron d electrons enables the low-energy electronic structure and angle-resolved photoemission spectroscopy spectra of iron-based superconductors to be modelled with unprecedented accuracy.

An experimental study of three-dimensional localization of ultracold atoms in controlled disorder provides evidence for behaviour that is consistent with Anderson localization, but incompatible with classical trapping.

A demonstration of the ability to control the flow of laser energy in a dense plasma by tuning the colour of multiple laser beams injected into it could be useful in the development of laser-driven fusion.

How quantum many-body systems relax from an initial non-equilibrium state is one of the outstanding problems in quantum statistical physics. A study combining an experimental approach for monitoring the dynamics of strongly correlated cold atoms with theoretical analysis now provides quantitative insights into the problem.

Mechanical oscillations of microscopic resonators have recently been observed in the quantum regime. This idea could soon be extended from localized vibrations to travelling waves thanks to a sensitive probe of so-called surface acoustic waves.

Individual molecules are now deterministically trapped in few-femtosecond laser pulses. This molecular conveyer belt may become a useful tool for probing ultrafast molecular dynamics.

A molecule can alter shape as it absorbs a photon. It is now shown that quantum effects can play an important role in this change leading to conformation rates hundreds of times faster than previously expected.

Superfluorescence—the emission of coherent light from an initially incoherent collection of excited dipoles—is now identified in a semiconductor. Laser-excited electron–hole pairs spontaneously polarize and then abruptly decay to produce intense pulses of light.

Probing the explosion of nitrous oxide ions in real time using high-harmonic radiation and infrared laser pulses now provides insight into the correlated dynamics of electrons and nuclei during photoionization.

Chiral superconducting states are expected to support a variety of exotic and potentially useful phenomena. Theoretical analysis suggests that just such a state could emerge in a doped graphene monolayer.

A novel mechanism for cooling nanomechanical objects has now been demonstrated. Optically excited electron–hole pairs produce a mechanical stress that damps the motion of a gallium arsenide membrane. In this way, the nanoscale resonator is cooled from room temperature to 4 K.

The transport measurements of an interacting fermionic quantum gas in an optical lattice provide a direct experimental realization of the Hubbard model—one of the central models for interacting electrons in solids—and give insights into the transport properties of many-body phases in condensed-matter physics.

Rapid particle acceleration is possible using a fixed-field alternating-gradient machine—but ‘scaling’ in its design has been necessary to avoid beam blow-up and loss. The demonstration now of acceleration in such a machine without scaling has positive implications for future particle accelerators.