Efficient demagnetization cooling of atoms and its limits

TL;DR

This paper demonstrates efficient demagnetization cooling of chromium atoms in an optical trap, reaching high densities and analyzing loss mechanisms, with potential to achieve quantum degeneracy solely through optical cooling.

Contribution

It provides experimental insights into demagnetization cooling of chromium atoms, identifying loss mechanisms and exploring its limits for reaching quantum degeneracy.

Findings

Achieved high-density chromium gas via demagnetization cooling.

Identified excited-state collisions as the main loss process.

Discussed potential for reaching degeneracy with optical cooling alone.

Abstract

Demagnetization cooling relies on spin-orbit coupling that brings motional and spin degrees of freedom into thermal equilibrium. In the case of a gas, one has the advantage that the spin degree of freedom can be cooled very efficiently using optical pumping. We investigate demagnetization cooling of a chromium gas in a deep optical dipole trap over a large temperature range and reach high densities up to $5\times 10^{19} m^{-3}$. We study the loss mechanism under such extreme conditions and identify excited-state collisions as the main limiting process. We discuss that in some systems demagnetization cooling has a realistic potential of reaching degeneracy by optical cooling only.