We have demonstrated a feasible experimental method to reduce the entropy of a targed ultracold quasidegenarate gas by transferring it in a reversible and controlled way to a second auxiliary gas.
We have employed an ultracold mixture of bosonic Potassium and Rubidium gases and a particular Species Selective Dipole Potential (SSDP). This SSDP trap exploits the fine structure of Rb (that remains substantially transparent to this beam) in order not to produce any mechanical effect on the Rb gas itself, while still producing a compression on the K gas.
This method has been employed to produce a BEC of 41K through an isothermal transformation. A selective compression reduces the K entropy while it preserves the total entropy of the system.
References:
Entropy exchange in a mixture of ultracold atoms
J. Catani, G. Barontini, G. Lamporesi, F. Rabatti, G. Thalhammer, F. Minardi, S. Stringari, and M. Inguscio
Phys. Rev. Lett. 103, 140401 (2009) [see also D. Stamper-Kurn, Physics 2, 80 (2009)].