Sympathetic cooling demonstrated with neutral atoms

17 Jun 2002

Sympathetic cooling, a process by which particles of one type cool particles of another type, has been demonstrated for the first time with neutral atoms.

Using a combination of lasers and magnetic fields, Christopher Myatt and his colleagues at NIST and the University of Colorado (303-492-2548) trapped a group of rubidium-87 atoms each having one of two possible values for spin, a quantity that describes how a particle responds to a magnetic field.

Atoms with one spin value are less tightly bound in the trap's magnetic fields and can be used to cool atoms with the other spin value since the weakly confined atoms could more easily escape the trap and carry away the energy given up by the second species during collisions. Applying this technique to the two rubidium spin species, the researchers have created, for the first time, two overlapping clouds of Bose-Einstein condensates, the new state of matter in which a group of atoms falls into exactly the same quantum state.

The researchers also observed that the BECs of the two rubidium species repelled each other. Sympathetic cooling may help enable Bose-Einstein condensation for rare isotopes, and may greatly facilitate comparative studies between fermions and bosons. Their results are reported in an upcoming article in Physical Review Letters.