  We demonstrate optical probing of spectrally resolved single Nd rare-earth
ions in yttrium orthovanadate. The ions are coupled to a photonic crystal
resonator and show strong enhancement of the optical emission rate via the
Purcell effect, resulting in near radiatively limited single photon emission.
The measured high coupling cooperativity between a single photon and the ion
allows for the observation of coherent optical Rabi oscillations. This could
enable optically controlled spin qubits, quantum logic gates, and spin-photon
interfaces for future quantum networks.
