Spin distillation cooling of ultracold Bose gases

TL;DR

This paper explores spin distillation cooling mechanisms in ultracold Bose gases, analyzing their physics, limitations, and potential for repeated cycles to achieve lower temperatures.

Contribution

It provides a detailed theoretical and numerical analysis of two spin distillation cooling mechanisms in different atomic species, expanding on previous experimental work.

Findings

Two distinct cooling mechanisms identified for ${}^{52}$Cr and ${}^{23}$Na.

Threshold magnetic field values determine the effectiveness of each mechanism.

Repeated spin distillation cycles can significantly reduce thermal atom fractions.

Abstract

We study the spin distillation of spinor gases of bosonic atoms and find two different mechanisms in ${}^{52}$Cr and $^{23}$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 [B. Naylor et al., 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.