Two photon interference using a single lead-vacancy center in diamond

The realization of quantum networks is based on the entanglement of stationary qubits via flying photons. Therefore, a fundamental requirement is a single photon source that can efficiently generate indistinguishable photons for the entanglement generation. The group-IV vacancy centers in diamond have emerged as promising candidates due to their spectral stability benefiting from inversion symmetry and long spin coherence time. In particular, the lead-vacancy (PbV) center exhibits transform-limited linewidths even above 10 K [1] and is predicted to have millisecond-scale spin coherence time near 9 K [2], making it suitable for scalable quantum networks.

Here, we report the indistinguishability of photons emitted from a single PbV center through a two-photon interference experiment, known as the Hong-Ou-Mandel (HOM) effect. Fluorescence from the PbV center was split into two paths and recombined at a HOM interferometer. Photon correlations were measured for parallel and orthogonal polarized schemes. In parallel polarization, a clear interference dip below 0.5 at zero time delay was observed, whereas for orthogonal polarization, the correlation function exceeded 0.5. These results confirm the generation of indistinguishable photons from a single PbV center, validating their potential as the solid-state quantum emitter.