Two-color grating magneto-optical trap for narrow-line laser cooling

Abstract

We demonstrate for the first time the two-color cooling and trapping of alkaline-earth atoms in a grating magneto-optical trap (gMOT). The trap is formed by a single incident laser beam together with four secondary beams that are generated via diffraction from a nanostructured wafer. A grating structure for a gMOT operating with strontium atoms is optimized and fabricated. We trap $10^6$ ${}^{88}$Sr atoms on the ${}^1$S${}_0$ $\to$ ${}^1$P${}_1$ transition at $461\mathrm{nm}$ and transfer $25\%$ of these atoms to the second cooling stage on the narrower ${}^1$S${}_0$ $\to$ ${}^3$P${}_1$ intercombination transition at $689\mathrm{nm}$, preparing a sample of $2.5\times 10^5$ atoms at $5\mu$K. These results demonstrate for the first time the applicability of the gMOT technology in conjunction with two widely differing wavelengths and enable the continued miniaturization of alkaline-earth based quantum technologies like optical atomic clocks.

7 pages, 5 figures