Narrow-line-mediated Sisyphus cooling in the ³P₂ metastable state of strontium

The ¹S₀ – ³P₀ clock transition in alkaline-earth(-like) atoms underpins state-of-the-art optical lattice clocks, atom interferometers, and quantum computing platforms. The continuous operation of these devices, which enhances clock and interferometer stability and enables uninterrupted qubit loading, requires a steady cold atom source compatible with coherent operation in the clock transition.

To address this challenge, we have developed a two-stage cooling and atom guiding scheme. Strontium atoms are first cooled on the ¹S₀ – ¹P₁ transition and subsequently optically pumped into the long-lived ³P₂ state for magnetic trapping. Narrow-line Doppler cooling on the ³P₂ - ³D₃ transition further cools the atoms to a few tens of μK, allowing efficient loading into a moving optical lattice that transports them away from the cooling light.

Here, we demonstrate efficient atom loading into the moving lattice by incorporating a Sisyphus potential in the ³D₃ state. This additional cooling mechanism enhances the narrow-line Doppler cooling, leading to a twofold increase in the atom flux transported by the moving lattice. This advancement represents a crucial step toward next-generation quantum devices with continuous operation.