High density loading and collisional loss of laser cooled molecules in an optical trap

TL;DR

This paper demonstrates the optical trapping of laser-cooled SrF molecules at high density, enabling the observation of molecule-molecule collisions and paving the way for evaporative cooling towards quantum degeneracy.

Contribution

It reports the first observation of molecule-molecule collisions in a bulk gas of laser-cooled molecules at high density and low temperature.

Findings

Achieved a peak density of approximately 3×10^10 cm^-3.

Measured a two-body loss rate coefficient of about 2.7×10^-10 cm^3/s.

Successfully cooled molecules to around 40 μK in an optical trap.

Abstract

We report optical trapping of laser-cooled molecules at sufficient density to observe molecule-molecule collisions for the first time in a bulk gas. SrF molecules from a red-detuned magneto-optical trap (MOT) are compressed and cooled in a blue-detuned MOT. Roughly 30% of these molecules are loaded into an optical dipole trap with peak number density $n_0 \approx 3\times 10^{10} \text{ cm}^{-3}$ and temperature $T\approx40$ $\mu$K. We observe two-body loss with rate coefficient $\beta = 2.7^{+1.2}_{-0.8}\times 10^{-10} \text{ cm}^3 \text{ s}^{-1}$. Achieving this density and temperature opens a path to evaporative cooling towards quantum degeneracy of laser-cooled molecules.