A Bose-Einstein condensate is a state of matter composed of very large number of particles, bosons, that have the same energy level, that of the lowest energy. In a superconductor, the Cooper pairs are the bosons and they form the condensate, but this is an unusual case where pairs are in a very strong interaction. The “actual” condensate that Einstein theoretically predicted in 1925 after the works of the Indian physicist Bose was only directly observed in 1995 in an atom gas. The gas had to be cooled [Refroidissement d’atomes] to a few billionths of a degree to absolute zero, thanks to very recent methods using lasers.
Just like superconductors, these gas condensates have spectacular properties such as the coherence of a unique wave, or superfluidity. These recent experimental developments have been at the origin of two Nobel Prizes, in 1997 for cooling atoms and in 2001 for the observation of gas condensates.
The field of research concerning gas condensates has developed a lot since the first discoveries in 1995, and is very promising today. For instance, a large number of research teams take advantage of the possibility of playing with various experimental parameters of the condensate in a controlled maner to study complex and still mysterious phenomena. This approach is called quantum simulation and it could provide a new means of understanding superconductivity.
Pictures of an atom gas speed profile at different temperatures. On the left: a classical cloud; in the middle: mix of a classical cloud with a condensate (central peak); on the right: pure condensate.
