Continuous Collective Strong Coupling of Strontium Atoms to a High Finesse Ring Cavity

We demonstrate continuous loading and strong collective coupling of atoms to a high finesse ring cavity. A series of spatially separated laser cooling stages delivers a continuous flux of 2.1(3)×107 Sr88 atoms/s into an intracavity magic wavelength lattice where the atoms are deterministically transported inside the ring cavity. We observe a continuous atom-cavity vacuum Rabi splitting, demonstrating the first steady-state strong collective coupling on a narrow linewidth atomic transition. This Letter opens the path to future continuous cold atom devices, such as a continuous wave superradiant laser with millihertz linewidth and low vibration sensitivity, enabling searches for new physics and technologies.