Predicted by Satyendra Nath Bose and Albert Einstein in 1925, a Bose– Einstein condensate is a system in which every atom occupies the same single-particle quantum state. Bose–Einstein condensation occurs at extremely low temperatures when the de Broglie wavelength of the atoms becomes comparable to the average distance between them. The remarkable properties of this so-called quantum-degenerate gas are the result of the weak interactions between the atoms, and this makes Bose condensates a rich testing ground for theories that describe the behaviour of matter at a fundamental level.
The first condensate was formed on 5 June 1995 when Eric Cornell, Carl Wieman and co-workers at the JILA laboratory in Boulder, Colorado, trapped and cooled a gas of rubidium-87 atoms to a temperature of 2 nK. A few months later Wolfgang Ketterle and co-workers at the Massachusetts Institute of Technology (MIT) made a sodium condensate, and since then Bose condensates have also been produced from lithium, hydrogen, helium, potassium, cesium and, very recently, ytterbium atoms.
In the September issue of Physics World Mark Edwards describes the latest advances in Bose-Einstein condensates and degenerate Fermi gases.