Three steps of Bose – Einstein condensation
Atoms are individuals. Sometimes, they loose their individuality and move together. This happens at low temperatures (nK), when their de Broglie
waves overlap. The whole atomic cloud becomes a single quantum object. Each of the atoms in the condensate (in blue) has the same quantum mechanical wave function, and so they all move as one. Atoms outside the condensate move faster and in all directions.
(Science 22/12/2005, Illustration: Steve Keller, reproduced with permission)
 Trapped atoms |
1. Atoms are trapped in special configurations of strong magnetic fields. |
 Trapped atoms are like top-spins in the center; of a quite shallow plate. |
 Laser beam |
2. The atomic cloud is cooled (atoms slow down) by absorbing and emitting photon quanta from counter - propagating laser beams. |
 Cooling ,by collisions: a ruby “atom” in "melassa" of photons (here polystyrene
balls). |
 |
3. The hottest atoms are removed, by flipping them with radio-frequency to a non-trapped (another Zeeman sublevel) state. |
 Cooling with evaporation, even using a hot air stream, is very effective |
http://www.physik.uni-mainz.de/quantum/bec/introduction/evaporativecooling.html