Volume 5 Issue 8, August 2009

The design and synthesis of novel materials is the rubric of both haute cuisine and materials physics — and in both there is great pleasure in creating and sharing the results of a new recipe.

Quantum mechanics predicts an infinite series of loosely bound states of three bosons, and the size of these trimers should scale with a factor of 22.7. This general result seems to be confirmed now in an experiment with an ultracold gas of potassium atoms.

There is growing evidence that solid helium-4 possesses superfluid properties, but the nature of this paradoxical phenomenon remains mysterious. The finding that helium-4 in its 'supersolid' form is stiffer than the normal solid adds to the enigma.

That ratchet-shaped structures patterned on a surface can direct the otherwise random motion of living cells across it is perhaps unsurprising. But that the direction of this motion depends on the type of cell is remarkable and potentially useful.

The case for the existence of intermediate-mass black holes, hundreds to thousands of times more massive than our Sun, has received a major boost — with implications for gravitational waves and clustered star formation.

Compact interferometers that exploit the wave character of atoms have the potential to outpace their optical counterparts in a number of sensing applications. A technique that harnesses the internal structure of atoms should bring such applications a step closer.

As with any viable technology, quantum-information processors have to deal with imperfections. The experimental implementation of a quantum-error correction code indicates how imperfections can be handled in a system where quantum information is encoded in continuous variables.

How far can you stretch an atomic wavefunction? An experiment demonstrates that the wavefunction of an ensemble of ultracold atoms trapped in an optical lattice can be reversibly expanded and shrunk over a distance of 1.5 mm.

An ion trap has been built and characterized in which the atom sits on the top of a stylus-like electrode. The design should find application in the construction of efficient light–matter interfaces and field sensors, where good access to the ion is crucial.

It is likely that antiferromagnetism has a role in the superconductivity of iron arsenide. But is the magnetism local, as described by the Heisenberg model, or itinerant, which is more in agreement with the Stoner model? The answer is both.

A picosecond technique for measuring the kinetic friction of a single benzene molecule on graphite reveals continuous Brownian motion, rather than the jerky hopping observed on most other surfaces.

The Stokes–Einstein equation relates the self-diffusion constant of a liquid with the mobility of its constituents. In water, however, the relation has to be modified for temperatures below ∼290 K. A combined experimental and numerical investigation suggests that this behaviour results from a specific change in the local water structure.

A reversed-field pinch is a toroidal device for magnetically confining plasmas, and a potential alternative to the tokamak for a future fusion reactor. Observations of the evolution of a reversed-field-pinch plasma towards a self-organized single-helicity state suggest that instability problems, which have previously hindered the development of these devices, could now be overcome.

A quantum computer requires quantum systems that are well-isolated from external perturbations, but which can still be easily manipulated with external fields. A scheme that uses spatially inhomogeneous fields to selectively address neutral-atom qubits while they are in field-insensitive superposition states satisfies these competing needs.

Bound macrodimers have now been directly observed for the first time. Macrodimers comprise two Rydberg atoms with a separation as large as 9 μm. The unique properties of macrodimers mean that they enable new experiments for investigating ultracold gases.

In 1970, Vitaly Efimov predicted that three interacting particles can form an infinite series of bound trimer states, even when none of the two-particle subsystems is stable. Experimental evidence for such an exotic state was obtained in 2006, but now an Efimov spectrum, containing two such states with the predicted scaling between them, has been observed.

Simultaneous coherent control of internal and motional states of a Bose–Einstein condensate has been demonstrated on an ‘atom chip’. The method should provide a route to generating many-particle entangled states, which are needed for entanglement-based technologies such as quantum-information processing or quantum-enhanced metrology.

The first evidence of supersolidity—the potential ability of solids to move without friction—in solid ⁴He was obtained in torsional-oscillator experiments. But later observations raised the possibility that the characteristic frequency changes were simply due to stiffening of the solid. Now, the results from a series of experiments comparing ³He and ⁴He rule out that explanation.

Lévy flights, a form of random walk, are quite common in nature. However only macroscopic signatures, obtained by averaging over many steps, have been measured so far. Now, the individual steps are observed directly as light scatters in a hot atomic vapour.

It is not surprising that a microfluidic channel whose walls have a ratchet-like structure can preferentially direct the flow of large particles in one direction. But a study of the movement of living cells through such channels provides the remarkable observation that the direction of preferred motion can be different for different species of cell.