Recently discovered quantum emitters in 2D materials have opened new prospects for integrated photonic devices for quantum information. Most of these applications require the emitted photons to be indistinguishable, which has remained elusive in 2D materials. Here we investigate two-photon interference of a quantum emitter generated in hexagonal boron nitride with use of an electron beam. We measure the correlations of zero-phonon-line photons in a Hong-Ou-Mandel interferometer under nonresonant excitation. We find that the emitted photons exhibit a partial indistinguishability of $0.44\pm 0.11$ in a 3-ns time window, which corresponds to a corrected value of $0.56\pm 0.11$ after imperfect emitter purity has been accounting for. The dependence of the Hong-Ou-Mandel visibility on the width of the postselection time window allows us to estimate the dephasing time of the emitter to be approximately $1.5$ ns, about half the limit set by spontaneous emission. A visibility greater than 90% is within reach with use of the Purcell effect with current 2D-material photonics.

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• Color centers
• Luminescence
• Optical quantum information processing
• Photonics
• Quantum interference effects
• Quantum optics
• Single photon sources
• Hexagonal boron nitride