Quantum interference of resonance fluorescence from Germanium-vacancy 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-transform-limited linewidth emission with $T_2/2T_1\sim0.86$ 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 $0.604\pm0.022$, 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.