Steady-state magneto-optical trap of fermionic strontium on a narrow-line transition

A steady-state magneto-optical trap (MOT) of fermionic strontium atoms operating on the 7.5-kHz-wide ¹S₀-³P₁ transition is demonstrated. This MOT contains 8.4×10⁷ atoms, a loading rate of 1.3×10⁷ atoms /s, and an average temperature of 12 μK. These parameters make it well suited to serve as a source of atoms for continuous-wave superradiant lasers operating on strontium's mHz-wide clock transition. Such lasers have only been demonstrated using pulsed Sr sources, limiting their range of applications. Our MOT makes an important step toward continuous operation of these devices, paving the way for continuous active optical clocks.