  Single-photon sources with high brightness and long coherence time are
promising qubit candidates for quantum technology. To this end, interfacing
emitters with high-finesse cavities is required, especially in the strong
coupling regime, which so far has only been limited to cryogenic temperatures.
Here, we experimentally demonstrate, at room temperature, strong coupling
between a single photon emitter and a novel cavity based on optical bound
states in the continuum. A remarkably large Rabi splitting of ~4 meV is
achieved thanks to the combination of the narrow linewidth and large oscillator
strength of emitters in hexagonal boron nitride and the efficient photon
trapping of the cavity. Our findings unveil new opportunities to realise
scalable quantum devices and explore fundamentally new regimes of strong
coupling in quantum systems at room-temperature.
