Doppler cooling to the Quantum limit

TL;DR

This paper investigates Doppler cooling near the quantum limit on narrow atomic transitions, revealing unique features like non-Gaussian momentum distributions and resonance divergence, supported by experiments and simulations.

Contribution

It provides experimental observations and theoretical analysis of Doppler cooling on narrow transitions, highlighting novel behaviors and improved techniques using a dipole trap.

Findings

Observation of non-Gaussian momentum distribution

Divergence of mean square momentum near resonance

Enhanced cooling with dipole trap by canceling clock shift

Abstract

Doppler cooling on a narrow transition is limited by the noise of single scattering events. It shows novel features, which are in sharp contrast with cooling on a broad transition, such as a non-Gaussian momentum distribution, and divergence of its mean square value close to the resonance. We have observed those features using 1D cooling on an intercombination transition in strontium, and compared the measurements with theoretical predictions and Monte Carlo simulations. We also find that for a very narrow transition, cooling can be improved using a dipole trap, where the clock shift is canceled.