Volume 8 Issue 4, April 2012

Confining liquid ³He in porous silica aerogel prepared with strong anisotropy stabilizes a state of axial superfluidity.

Squeezed states push the limits of quantum measurement precision, but observing them is never straightforward. In spin-1 Bose–Einstein condensates, an elegant algebra reveals squeezed states that would otherwise go unnoticed.

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.

Optical computers will be more interesting if they take advantage of phenomena that are unique to optics. In this respect, telecommunications hardware might have something to offer.

Migrating cells are capable of actively opposing external forces. A study of the polymers that mediate cell motility indicates that they effect this response by branching where bent under force.

The long-term promises of quantum simulators are far-reaching. The field, however, also needs clearly defined short-term goals.

Experiments with ultracold quantum gases provide a platform for creating many-body systems that can be well controlled and whose parameters can be tuned over a wide range. These properties put these systems in an ideal position for simulating problems that are out of reach for classical computers. This review surveys key advances in this field and discusses the possibilities offered by this approach to quantum simulation.

Experimental progress in controlling and manipulating trapped atomic ions has opened the door for a series of proof-of-principle quantum simulations. This article reviews these experiments, together with the methods and tools that have enabled them, and provides an outlook on future directions in the field.

Quantum optics has played an important role in the exploration of foundational issues in quantum mechanics, and in using quantum effects for information processing and communications purposes. Photonic quantum systems now also provide a valuable test bed for quantum simulations. This article surveys the first generation of such experiments, and discusses the prospects for tackling outstanding problems in physics, chemistry and biology.

Lithographically fabricated micrometre-scale superconducting circuits exhibit behaviour analogues to natural quantum entities, such as atom, ions and photons. Large-scale arrays of such circuits hold the promise of providing a unique route to quantum simulation. Recent progress in technology and methodology are reviewed here, and prospects and challenges discussed.

An experiment demonstrates that the motion of so-called skyrmions—topologically quantized magnetic whirls—causes an emergent electric field that inherits the topological quantization of the skyrmions and is directly visible in the Hall effect.

Squeezed states—which permit precision beyond the scope of Heisenberg’s uncertainty relation—are well established for spin-1/2 particles. Now an elegant demonstration of squeezing in spin-1 condensates generalizes the criteria for squeezed states to higher spin dimensions.

One proposed explanation of unconventional superconductivity involves describing it in terms of a crossover from a conventional superconducting state to a Bose–Einstein condensate state. Angle-resolved photoelectron measurements of an iron chalcogenide superconductor could provide evidence for such crossover behaviour.

The degree to which an electrical current is spin polarized is usually determined by how easily it travels across an interface with a magnetic contact. By using nonlinear interactions between spin and charge in graphene, the polarization of spin currents can be measured without magnetic contacts.

Liquid ³He in silica aerogel exhibits no trace of the chiral superfluid phase present in bulk ³He. Stretching the aerogel axially introduces an anisotropy that stabilizes the chiral phase, supporting a transition to a new disordered phase at low temperatures.

Magnetic reconnection is a process by which the field lines of a magnetized plasma undergo dramatic realignment, releasing large amounts of energy. Large-scale simulations of reconnection events in the Earth’s magnetosphere suggest that this process takes place over much greater distances than previously expected.

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.

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.

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.

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.

Before the advent of digital computers, sophisticated orreries were used to predict the positions and motions of astronomical bodies. Today, we are witnessing the renaissance of devices that simulate, rather than calculate, the evolution of complex many-body systems. Quantum simulators — which use one controllable quantum system to investigate the behaviour and properties of another, less accessible one — hold the promise of tackling problems that are too demanding for classical computers. Over the past few years, significant progress has been made in a number of experimental fields, as reviewed in this Insight, which also considers where quantum simulation might take us.