Spin distillation cooling of ultracold Bose gases

Abstract

We study the spin distillation of spinor gases of bosonic atoms and find two different mechanisms in $${}^{52}$$ 52 Cr and $$^{23}$$ 23 Na atoms, both of which can cool effectively. The first mechanism involves dipolar scattering into initially unoccupied spin states and cools only above a threshold magnetic field. The second proceeds via equilibrium relaxation of the thermal cloud into empty spin states, reducing its proportion in the initial component. It cools only below a threshold magnetic field. The technique was initially demonstrated experimentally for a chromium dipolar gas (Naylor et al. in Phys Rev Lett 115:243002, 2015), whereas here we develop the concept further and provide an in-depth understanding of the required physics and limitations involved. Through numerical simulations, we reveal the mechanisms involved and demonstrate that the spin distillation cycle can be repeated several times, each time resulting in a significant additional reduction of the thermal atom fraction. Threshold values of magnetic field and predictions for the achievable temperature are also identified.

Dipolar physics: A review of experiments with magnetic quantum gases

“…[587] that the purification of a BEC by spin-filtering could be extended to non-dipolar species by using spin-dependent contact interactions and spin-exchange interactions. Both the dipolar and the non-dipolar cooling schemes were theoretically explored in [588]. A related cooling scheme was demonstrated with Rb atoms [589].…”

Dipolar physics: a review of experiments with magnetic quantum gases

“…It was suggested in [594] that the purification of a BEC by spin-filtering could be extended to non-dipolar species by using spin-dependent contact interactions and spin-exchange interactions. Both the dipolar and the non-dipolar cooling schemes were theoretically explored in [595]. A related cooling scheme was demonstrated with Rb atoms [596].…”