Everyday macroscopic objects follow the laws of classical mechanics. But for microscopic objects, such as atoms or nuclei, the wave character of their dynamics has to be taken into account within the framework of quantum mechanics. Wave-like behaviour can show up in various ways, and one of the most striking is the tunnelling effect. Similarly, events that are prohibited due to some other dynamical constraints can occur via a process known as dynamical tunnelling. Indeed, tunnelling plays a major role in a variety of physical phenomena, ranging from alpha-particle radioactivity to the current-voltage characteristics of transistors.

Now two independent teams at the University of Texas, and at the University of Queensland in Australia together with the National Institute of Standards and Technology in Gaithersburg, US, have studied the tunnelling of atoms in the presence of chaos. The work was made possible by sophisticated tools that have recently been developed to study cold atoms and Bose-Einstein condensates (D Steck et al. 2001 Science 293 274; W Hensinger et al. 2001 Nature 412 52).

In the September issue of Physics World, Amaury Mouchet of the Université François Rabelais and Denis Ullmo of the Laboratoire de Physique Théorique et Modéles Statistiques, France, reveal how chaos can lend a hand to different kinds of tunnelling.