Bose-Einstein condensation occurs when a gas of atoms is cooled until the de Broglie wavelength of the atoms becomes comparable with the inter-atom separation. The atoms all collapse into the same quantum ground state and the resulting condensate exhibits many unusual quantum properties such as superfluidity.

The first condensate was created in a gas of rubidium-87 in 1995 and since then condensates have also be produced in lithium, sodium, hydrogen, helium and potassium. Eric Cornell, Wolfgang Ketterle and Carl Wieman shared the 2001 Nobel Prize in Physics for their work on Bose condensates. Several groups have also managed to create so-called quantum degenerate Fermi gases - the equivalent of Bose-Einsetin condensation for atoms that obey Fermi-Dirac statistics.

Since 1995 the majority of condensates have been produced in rubidium. Now Rudi Grimm and co-workers at the University of Innsbruck have managed to produce a caesium condensate for the first time. They observed the Bose-Einstein condensation of caesium at a temperature of 45  nanokelvin and managed to produce pure condensates containing some 20 000 caesium atoms. Caesium condensates should be particularly useful for studying degenerate quantum gases in two dimensions.