In a Bose-Einstein condensate a gas of atoms is cooled until the de Broglie wavelength of the atoms exceeds the inter-atom spacing. If the atoms are bosons - that is, if they have a "spin" of 0, h/2p, 2(h/2p), 3(h/2p) and so on, where h is the Planck constant - they all collapse into the same quantum ground state. This gives the condensate many unusual quantum properties.

In quantum information the ability of a quantum particle - such as an atom or a photon - to be in two or more quantum states at the same time can be used to perform certain computational tasks much faster than would be possible with a conventional or classical computer. As the number of quantum particles increases, the quantum computer outperforms the classical computer by larger and larger factors. A key requirement for quantum computation is that the particles must be in an entangled state: in such a state the correlations between the particles are much stronger than any classical correlations. However, entangled states are difficult to prepare and maintain.

Zoller and co-workers show theoretically how a specially prepared laser pulse could be used to entangle all the atoms in a condensate. The pulse has the property that its area is p/2. The largest number of particles that has been entangled so far is four. However, the Innsbruck-Aarhus team claim that their technique could eventually be used to entangle any number of atoms.