Volume 4 Issue 6, June 2008

Dark solitons in Bose–Einstein condensates have been made to live long enough for their dynamical properties to be observed. They might serve as a sensitive probe of the rich physics at the mesoscale.

The most precise calculations yet of how two quarks locked in a bound state annihilate have been achieved using lattice quantum chromodynamics — and signal a curious discrepancy.

Gravitational wave detectors based on laser interferometry have reached an incredible level of sensitivity. But to develop to the level needed to explore the Universe, the next generation of detectors will probably need to use squeezed light.

Many have reported evidence for a quantum spin liquid state — in which quantum fluctuations prevent spin order — but thermodynamic evidence has been lacking, until now. Although it points the way, is it enough?

Unprecedented control over the superposition of electronic states in a 'quantum corral', exerted by changing the position of a single atom within it, provides a powerful tool for studying the quantum behaviour of matter.

The standard assumption in thermodynamics that a sufficiently slow change of external parameters will generate no entropy turns out to be wrong for low-dimensional, gapless systems. Its breakdown may be tested with ultracold gases.

The development of compact plasma accelerators, enabled by the advent of high-power lasers, could revolutionize the use of particle beams. This review presents the physical principles that underlie such devices and provides an outlook on the possibilities.

Unprecedented control over the superposition of electronic states of a ‘quantum coral’, by changing the position of a single atom within it, provides a powerful tool for studying the quantum behaviour of matter.

Spins in a two-dimensional triangular lattice are geometrically frustrated and cannot form an ordered ground state. Instead, a spin-liquid state is expected, and now thermodynamic measurements suggest that a spin liquid exists down to the lowest temperatures.

Like their classical counterparts, quantum computers can, in theory, cope with imperfections—provided that these are small enough. The regime of fault-tolerant quantum computing has now been reached for a system based on trapped ions, in which a gate operation for entangling qubits has been implemented with a fidelity exceeding 99%.

Four electrons in a semiconductor quantum dot exhibit similar correlation effects to those found in a molecule. Excitations of these electrons can be probed by inelastic light scattering, which reveals a decoupling of their rigid rotational motion from their spin excitations.

Substantial improvements, through the use of squeezed light, in the sensitivity of a prototype gravitational-wave detector built with quasi-free suspended optics represents the next step in moving such devices out of the lab and into orbit.

When a thermodynamic system is changed sufficiently slowly, entropy is generally conserved and the process is adiabatic, and therefore reversible. However, this adiabaticity does not seem to hold for low-dimensional systems with a high-density of low-energy states.

A proposal describes how to detect topologically ordered states of ultracold matter in an optical lattice, and shows how these exotic states, which strongly correlated quantum systems can exhibit, could be harnessed for practical applications, such as robust quantum computation.

The analysis of the interference fringes generated by initially independent one-dimensional Bose condensates reveals contributions of both quantum noise and thermal noise, advancing our fundamental understanding of quantum states in interacting many-body systems.

Solitons are encountered in a wide range of nonlinear systems, from water channels to optical fibres. They have also been observed in Bose–Einstein condensates, but only now have such ‘ultracold solitons’ been made to live long enough for their dynamical properties to be studied in detail.

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