Resonance fluorescence from a quantum emitter is an ideal source to extract indistinguishable photons. By using the cross-polarization to suppress the laser scattering, we observed resonance fluorescence from GeV color centers in diamond at cryogenic temperature. The Fourier-transform-limited line width emission with T 2/2T 1 ∼ 0.86 allows for two-photon interference based on single GeV color center. Under pulsed excitation, the separated photons exhibit a Hong–Ou–Mandel quantum interference above classical limit, whereas the continuous-wave excitation leads to a coalescence time window of 1.05 radiative lifetime. In addition, we demonstrated a single-shot readout of spin states with a fidelity of 74%. Our experiments lay down the foundation for building a quantum network with GeV color centers in diamond.

Resonance fluorescence from a quantum emitter is an ideal source to extract indistinguishable photons. By using the cross polarization to suppress the laser scattering, we observed resonance fluorescence from GeV color centers in diamond at cryogenic temperature. The Fourier-transformlimited linewidth emission with T2/2T1 ∼ 0.86 allows for two-photon interference based on single GeV color center. Under pulsed excitation, the 24 ns separated photons exhibit a Hong-Ou-Mandel visibility of 0.604 ± 0.022, while the continuous-wave excitation leads to a coalescence time window of 1.05 radiative lifetime. Together with single-shot readout of spin states, it paves the way towards building a quantum network with GeV color centers in diamond.