  Efficient coupling of optically active qubits to optical cavities is a key
challenge for solid-state-based quantum optics experiments and future quantum
technologies. Here we present a quantum photonic interface based on a single
Tin-Vacancy center in a micrometer-thin diamond membrane coupled to a tunable
open microcavity. We use the full tunability of the microcavity to selectively
address individual Tin-Vacancy centers within the cavity mode volume. Purcell
enhancement of the Tin-Vacancy center optical transition is evidenced both by
optical excited state lifetime reduction and by optical linewidth broadening.
As the emitter selectively reflects the single-photon component of the incident
light, the coupled emitter-cavity system exhibits strong quantum nonlinear
behavior. On resonance, we observe a transmission dip of 50 % for low incident
photon number per Purcell-reduced excited state lifetime, while the dip
disappears as the emitter is saturated with higher photon number. Moreover, we
demonstrate that the emitter strongly modifies the photon statistics of the
transmitted light by observing photon bunching. This work establishes a
versatile and tunable platform for advanced quantum optics experiments and
proof-of-principle demonstrations towards quantum networking with solid-state
qubits.
