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.

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Genuine high-dimensional (HD) quantum steering was recently proposed for certifying HD entanglement in the one-sided device-independent setting, as quantified by the Schmidt number [Phys. Rev. Lett. 126, 200404 (2021)PRLTAO0031-900710.1103/PhysRevLett.126.200404]. As one of the central challenges in the steering test is the tolerated noise threshold, here we develop a more robust method for certifying genuine HD steering in noisy environments. We derive genuine HD steering criteria using multiple mutually unbiased bases, surpassing the previous restriction of only two measurement settings. Although the present multisetting criteria are not tight, we theoretically show that they are more robust to noise than the tight two-setting criteria. To test the practicality of our method under realistic conditions, we report an experimental demonstration using photonic orbital angular momentum entangled states in dimensions d = 3 , 4 , 5 . Our work offers a more robust way to witness the entanglement dimension in practical one-sided device-independent quantum information processing.