Sub-Doppler cooling of bosonic strontium in a two-color MOT

TL;DR

This paper demonstrates a two-color magneto-optical trap for bosonic strontium that achieves sub-Doppler cooling, reaching temperatures as low as 45 μK, and provides precise measurements of transition frequencies.

Contribution

It introduces a continuous two-color MOT for strontium with sub-Doppler cooling and accurately measures a key transition frequency, advancing cold atom trapping techniques.

Findings

Achieved sub-Doppler cooling down to 45 μK.

Measured the (5s5p)3P2-(5s5d)3D3 transition frequency with high precision.

Observed bimodal momentum distribution indicating effective cooling mechanisms.

Abstract

We report a two-color magneto-optical trap that continuously operates on the $\mathrm{(5s^2)\:^1S_0-(5s5p)\:^1P_1}$ and $\mathrm{(5s5p)\:^3P_2-(5s5d)\:^3D_3}$ transitions in $\mathrm{^{88}Sr}$. Owing to the sub-Doppler cooling from the metastable $\mathrm{(5s5p)\:^3P_2}$ state, a bimodal momentum distribution is observed, with the cold part of the ensemble reaching a temperature of 105 $\mathrm{\mu}$K. A detailed simulation is established to explain the data. The absolute frequency of the $\mathrm{(5s5p)\:^3P_2-(5s5d)\:^3D_3}$ transition is measured to be 603 976 473 ${\pm}$ 2 MHz using a frequency comb, improving the literature value. The accompanying magnetic trap is characterized, and is shown to contribute to the sequential production of ensembles with temperatures down to 45 $\mathrm{\mu}$K.