Strong coupling of dipole trapped atomic ensembles to a ring cavity

Cavity quantum electrodynamics systems using atoms in resonant optical cavities are central elements of many applications such as quantum networks and quantum-enhanced sensing. We present a novel experimental setup that achieves strong spatial mode-matching between a resonant mode of a triangular ring resonator and an ensemble of ultracold atoms trapped in an optical dipole trap. We realise a large-volume, 0.5\,mK deep cavity-assisted optical dipole trap from a laser beam of modest power locked to a resonant mode of the cavity through the intracavity power build-up effect, allowing efficient loading of the trap from a magneto-optical trap. We observe dipole trapping of atoms through the vacuum Rabi splitting of the transmission spectrum of a weak probe beam near resonant with the cavity, which demonstrates collective strong coupling of the ensemble of atoms to the cavity after the magneto-optical trap is turned off. The work paves the way for a highly suitable platform for cavity-assisted quantum sensing of magnetic and electric fields.