Narrow-line-mediated Sisyphus cooling in the ${}^3{\mathrm{P}}_2$ metastable state of strontium

We demonstrate narrow-line-mediated Sisyphus cooling of magnetically trapped strontium (Sr) in the $5s5p{}^3{\text{P}}_2$ state. A 641 nm standing-wave, blue-detuned from the $5s4d{}^3{\text{D}}_3$$\to$ $5p4d{}^3{\text{F}}_4$ transition, creates a dissipative optical lattice in the ${}^3{\text{D}}_3$ state. By combining Doppler cooling and Sisyphus cooling on the $5s5p{}^3{\text{P}}_2$$\to$ $5s4d{}^3{\text{D}}_3$ transition at 2.92 $\mu$m, we observed efficient cooling of magnetically trapped atoms. By optically pumping the atoms to the $5s5p{}^3{\text{P}}_0$ state, we facilitate continuous outcoupling via a moving optical lattice with two fold improvement in atom number. Our scheme applies to next-generation quantum sensors using continuous ultracold atomic beams.