Evaporative cooling of a small number of atoms in a single-beam microscopic dipole trap

TL;DR

This paper reports the successful evaporative cooling of a small number of rubidium atoms in a microscopic dipole trap, achieving near-quantum degeneracy within a few seconds.

Contribution

It demonstrates that evaporative cooling and scaling laws are effective even with only a few hundred atoms in a microscopic trap.

Findings

Reduced atom sample from 800 to 40 atoms at ultracold temperatures

Achieved phase-space density close to quantum degeneracy

Validated kinetic model against experimental data

Abstract

We demonstrate experimentally the evaporative cooling of a few hundred rubidium 87 atoms in a single-beam microscopic dipole trap. Starting from 800 atoms at a temperature of 125microKelvins, we produce an unpolarized sample of 40 atoms at 110nK, within 3s. The phase-space density at the end of the evaporation reaches unity, close to quantum degeneracy. The gain in phase-space density after evaporation is 10^3. We find that the scaling laws used for much larger numbers of atoms are still valid despite the small number of atoms involved in the evaporative cooling process. We also compare our results to a simple kinetic model describing the evaporation process and find good agreement with the data.