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Physical Review Applied

Two-Photon Interference from a Quantum Emitter in Hexagonal Boron Nitride

Clarisse Fournier, Sébastien Roux, Kenji Watanabe, Takashi Taniguchi, Stéphanie Buil, Julien Barjon, Jean‐Pierre Hermier, Aymeric Delteil

Published Apr 27, 2023• 62 citations
Publisher

Abstract

Indistinguishable single photons are a key requirement for most applications in optical quantum information. However, this feature has remained elusive among two-dimensional materials, primarily due to insufficient coherence of emitters. Here the authors controllably generate a spectrally narrow and stable single-photon source in an h-BN crystal by electron-beam irradiation, and demonstrate Hong-Ou-Mandel interference of the emitted photons, which is a signature of indistinguishability. These results enable practical applications in integrated quantum photonics based on two-dimensional materials.

DOI
10.1103/physrevapplied.19.l041003

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Quantum emitters in hexagonal boron nitride (hBN) have emerged as a promising solid-state platform for quantum technology applications. However, a persistent challenge in the field is the unclear origin of many observed emission lines, particularly in the visible range, which can be difficult to distinguish from signals arising from organic or process-induced contamination during sample preparations and handling. This ambiguity limits both the reproducibility of emitter generation and the reliable identification of truly intrinsic quantum defects. This work provides a step-by-step framework to assess whether quantum emitters in electron-irradiated hBN are associated with organic contaminants introduced during sample preparation. We employ hyperspectral imaging, thermal annealing, and oxygen plasma etching to investigate the origin of the green-yellow emitters in electron-irradiated hBN. The combined results not only rule out organic contamination as the source of emission but also provide insight into the spectral variability, thermal stability, and vertical localization of the emitters generated in electron-irradiated hBN that was created without any pre- or post-processing. In addition, our experiments demonstrate the feasibility of creating stable emitters in hBN with thicknesses below 10 nm. These findings provide practical guidance for the identification and controlled implementation of hBN-based single-photon emitters in quantum photonic devices.

physics.opticsCross-listedarXiv:2605.12663•May 14, 2026
Indistinguishable single photons are a key requirement for most applications in optical quantum information. However, this feature has remained elusive among two-dimensional materials, primarily due to insufficient coherence of emitters. Here the authors controllably generate a spectrally narrow and stable single-photon source in an h-BN crystal by electron-beam irradiation, and demonstrate Hong-Ou-Mandel interference of the emitted photons, which is a signature of indistinguishability. These results enable practical applications in integrated quantum photonics based on two-dimensional materials.
Optically active defects in hexagonal boron nitride (hBN) have become amongst the most attractive single-photon emitters in the solid state, owing to their high-quality photophysical properties, combined with the unlimited possibilities of integration offered by the host van der Waals material. In particular, the B centres, with their narrow linewidth, low wavelength spread and controllable positioning, have raised a particular interest for integrated quantum photonics. However, to date, either their excitation or their detection has been performed non-resonantly due to the difficulty of rejecting the backreflected laser light at the same wavelength, thereby preventing to take full benefit from their high coherence in quantum protocols. Here, we make use of narrow-linewidth emitters integrated in a hybrid metal-dielectric structure to implement cross-polarisation laser rejection. This allows us to observe resonantly scattered photons, with associated experimental signatures of optical coherence in both continuous-wave (cw) and pulsed regimes, respectively the Mollow triplet and Hong-Ou-Mandel interference from zero-phonon-line emission. The two-photon interference visibilities of 0.93−0.21+0.070.9{3}_{-0.21}^{+0.07}0.93−0.21+0.07​ and 0.92−0.26+0.080.9{2}_{-0.26}^{+0.08}0.92−0.26+0.08​ we measured for two emitters demonstrate the potential of B centres in hBN for applications to integrated quantum information. Single-photon sources in van der Waals materials offer new perspectives of integration for quantum information applications. Here, the authors implement resonance fluorescence of a single colour centre in hBN, a quantum optics regime that simultaneously allows for emitter coherent control and generation of indistinguishable photons.
Single-photon sources are crucial components for building quantum networks and communications, but their optical coherent control remains a significant challenge in the development of quantum technologies. Recently, single-photon sources in atomically thin 2D materials such as transition metal dichalcogenides and van der Waals materials have emerged as promising solid-state quantum light emitters [1]. Hexagonal boron nitride (hBN) is a 2D insulator, which hosts optically active states in its band gap that efficiently emit single photons even at room temperature. The wide range of emission wavelengths, narrow emission lines, and convenient tunability of these hBN emitters make them particularly interesting for quantum sensing and wavelength division multiplexed quantum communications. They can also be found in commercially available nanocrystals, making them ideal for creating large arrays of single-photon emitters [2] and efficient coupling to photonic structures, such as 3D-printed microlenses [3].
Sources of pure and indistinguishable single-photons are critical for near-future optical quantum technologies. Recently, color centers hosted by two-dimensional hexagonal boron nitride (hBN) have emerged as a promising platform for high luminosity room temperature single-photon sources. Despite the brightness of the emitters, the spectrum is rather broad and the single-photon purity is not sufficient for practical quantum information processing. Here, we report integration of such a quantum emitter hosted by hBN into a tunable optical microcavity. A small mode volume of the order of λ 3 allows us to Purcell enhance the fluorescence, with the observed excited state lifetime shortening. The cavity significantly narrows the spectrum and improves the single-photon purity by suppression of off-resonant noise. The complete device, including all optics, driving electronics, and control units, is compact and integrated in a small volume of 10 × 10 × 10 cm 3, allowing for portable usage in mobile applications.
The generation of indistinguishable photons is a key requirement for solid-state quantum emitters as a viable source for applications in quantum technologies. Restricting the dimensions of the solid-state host to a size well below the wavelength of light emitted by a defect-center enables efficient external optical coupling, for example for hybrid integration into photonic devices. However, stringent restrictions on the host dimensions result in severe limitations on the spectral properties reducing the indistinguishability of emitted photons. Here, we demonstrate two-photon interference from two negatively-charged Silicon-Vacancy centers located in remote nanodiamonds. The Hong-Ou-Mandel interference efficiency reaches 61% with a coalescence time window of 0.35 ns. We furthermore show a high yield of pairs of Silicon-Vacancy centers with indistinguishable optical transitions. Therefore, our work opens new paths in hybrid quantum technology based on indistinguishable single-photon emitters in nanodiamonds.
Collective light emission from many-body quantum systems is a cornerstone of quantum optics, yet its implementation in solid-state platforms operating under ambient conditions remains highly challenging. Large-bandgap van der Waals materials such as hexagonal boron nitride (hBN) host stable room-temperature single-photon emitters with narrow linewidths across a broad spectral range. However, cooperative radiative effects in this system have not been previously explored. Here we demonstrate collective emission from quantum-emitter ensembles in hBN layers when the emitters are nearly indistinguishable and positioned within a sub-wavelength proximity. Using confocal microscopy and a Hanbury Brown-Twiss (HBT) configuration, we identify both isolated emitters and ensembles activated by localized electron-beam irradiation. Time-resolved photoluminescence measurements reveal a superlinear intensity enhancement and a pronounced acceleration of the radiative decay in tightly confined ensembles, with lifetimes approaching the temporal resolution of our experimental system (about 500 ps), compared to approximately 1.85 ns for single emitters or large, spatially extended ensembles. Complementary second-order photon-correlation measurements exhibit sub-Poissonian antidip consistent with emission from a few indistinguishable emitters. The simultaneous observation of lifetime shortening and enhanced emission provides direct evidence of cooperative emission at room temperature, achieved without optical cavities or cryogenic cooling. These results establish optically active defect ensembles in hBN as a scalable solid-state platform for engineered collective quantum optics in two-dimensional materials, opening avenues toward ultrabright superradiant light sources and nonclassical photonic states for quantum technologies.
Quantum emitters in hexagonal boron nitride (hBN) have emerged as a promising solid-state platform for quantum technology applications. However, a persistent challenge in the field is the unclear origin of many observed emission lines, particularly in the visible range, which can be difficult to distinguish from signals arising from organic or process-induced contamination during sample preparations and handling. This ambiguity limits both the reproducibility of emitter generation and the reliable identification of truly intrinsic quantum defects. This work provides a step-by-step framework to assess whether quantum emitters in electron-irradiated hBN are associated with organic contaminants introduced during sample preparation. We employ hyperspectral imaging, thermal annealing, and oxygen plasma etching to investigate the origin of the green-yellow emitters in electron-irradiated hBN. The combined results not only rule out organic contamination as the source of emission but also provide insight into the spectral variability, thermal stability, and vertical localization of the emitters generated in electron-irradiated hBN that was created without any pre- or post-processing. In addition, our experiments demonstrate the feasibility of creating stable emitters in hBN with thicknesses below 10 nm. These findings provide practical guidance for the identification and controlled implementation of hBN-based single-photon emitters in quantum photonic devices.