Cooling of a Bose-Einstein condensate by spin distillation

We propose and experimentally demonstrate a new cooling mechanism leading to purification of a Bose-Einstein condensate (BEC).
arXiv:1505.05098 (2015) / Phys. Rev. Lett. 115, 243002 (2015)

Our scheme starts with a BEC polarized in the lowest energy spin state. Spin excited states are thermally populated by lowering the single particle energy gap set by the magnetic field. Then, these spin-excited thermal components are filtered out, which leads to an increase of the BEC fraction. We experimentally demonstrate such cooling for a spin 3 52Cr dipolar BEC.

Our scheme should be applicable to Na or Rb, with the perspective to reach temperatures below 1 nK.

a) Principle of the proposal. b) Density profiles after depolarization and Stern Gerlach procedure showing a 52Cr BEC forming only in ms = −3. c) Purification of a 52 Cr BEC.