Researchers Demonstrate Collective Emission from Hexagonal Boron Nitride Emitter Ensembles

Scientists are increasingly focused on achieving collective light emission in solid-state materials at room temperature, a feat historically difficult to realise. Igor Khanonkin, Amir Sivan (Technion – Israel Institute of Technology) and Le Liu, alongside Johannes Eberle, Kenji Watanabe (National Institute for Materials Science, NIMS) and Takashi Taniguchi, report the observation of cooperative emission from quantum emitters within hexagonal boron nitride layers. Their work, detailed in this paper, is significant because it demonstrates superradiance , enhanced and accelerated light emission , from these defect ensembles without the need for cryogenic cooling or complex optical cavities. This breakthrough establishes hBN as a promising, scalable platform for developing advanced photonic technologies, including ultrabright light sources and novel quantum states?

The research team identified and activated these ensembles using confocal microscopy and a Hanbury Brown-Twiss configuration, employing localized electron-beam irradiation to create nearly indistinguishable emitters in close proximity. Time-resolved photoluminescence measurements revealed a superlinear intensity enhancement and a pronounced acceleration of radiative decay within these tightly confined ensembles, with lifetimes approaching the limits of their experimental system at approximately 500ps. This represents a significant reduction compared to the 1.85ns lifetime observed in single emitters or larger, spatially extended ensembles.

The study establishes that these accelerated decay rates and enhanced emission intensities provide direct evidence of cooperative emission, a phenomenon where multiple emitters act collectively to amplify light output. Complementary second-order photon-correlation measurements further confirmed this cooperative behaviour, exhibiting sub-Poissonian antidips consistent with emission originating from a few indistinguishable emitters. Researchers meticulously compared single B-centers, exhibiting a radiative lifetime of approximately 1.85ns, with localized ensembles containing an estimated 1, 2, 3, and 4 emitters, observing a systematic and monotonic acceleration of radiative decay as the number of emitters increased. This detailed analysis underscores the collective nature of the observed emission and its dependence on the number of interacting emitters within the ensemble.

This work establishes optically active defect ensembles in hBN as a scalable solid-state platform for engineered collective optics in two-dimensional materials. The ability to achieve cooperative emission at room temperature, without complex experimental setups, opens avenues toward ultrabright superradiant light sources and the generation of nonclassical photonic states. These advancements have significant implications for quantum technologies, potentially enabling the development of more efficient and robust quantum devices. The team’s findings demonstrate the potential of hBN-based emitters to serve as building blocks for future quantum photonic circuits and applications, paving the way for innovative technologies in quantum communication and sensing.

HBN Defect Ensemble Mapping and Characterisation reveals critical

Scientists investigated collective light emission from ensembles of B-center defects within hexagonal boron nitride (hBN) layers at room temperature. The study employed confocal microscopy and a Hanbury Brown-Twiss (HBT) configuration to identify and characterise both isolated emitters and ensembles activated by localised electron-beam irradiation. Researchers utilised scanning electron microscopy (SEM) to image the hBN flakes following irradiation, revealing activated defect sites and enabling the identification of regions containing ensembles. Wide-field confocal photoluminescence (PL) scans then mapped the spatial distribution of these defect ensembles, pinpointing areas of enhanced emission.

To quantify radiative dynamics, time-resolved PL measurements were performed, revealing a superlinear intensity enhancement and a pronounced acceleration of radiative decay within tightly confined ensembles. The team observed lifetimes approaching the temporal resolution limit of approximately 500ps, a significant reduction compared to the 1.85ns lifetime measured for single emitters or larger, spatially extended ensembles. Complementary second-order photon-correlation measurements demonstrated sub-Poissonian antidips, indicative of emission originating from a few indistinguishable emitters. This combination of lifetime shortening and enhanced emission provided direct evidence of cooperative emission occurring at room temperature, achieved without the need for optical cavities or cryogenic cooling.

The work systematically compared single B-centers, exhibiting a radiative lifetime of τ ≈1.85ns, with localised ensembles containing estimated numbers of 1, 2, 3, and 4 emitters. This comparison resolved a monotonic acceleration of radiative decay, accompanied by superlinear enhancement of emission intensity. Extended regions subjected to prolonged irradiation (electron dose of 4.5 × 10¹³), generating high densities of B-centers, were also examined. SEM imaging and PL mapping confirmed the presence of spatially diffuse emission, but time-resolved PL measurements revealed mono-exponential decays of 1.85ns, identical to isolated single emitters, demonstrating the absence of cooperative effects in large, extended ensembles.

Researchers further refined the experimental setup by performing multiple localised irradiations, creating tightly spaced defect sites. Confocal PL maps revealed the spatial arrangement of these emitters, allowing for a direct comparison between spatially separated and sub-wavelength proximity configurations. Second-order photon-correlation measurements of tightly spaced emitters exhibited a sub-Poissonian bunching antidip of g(2)(0) ≈0.62, while time-resolved PL traces showed an accelerated decay of 1.25ns, contrasting with the 1.84ns decay observed for spatially separated emitters. This innovative approach established a solid-state, room-temperature realisation of collective emission in a two-dimensional material platform, paving the way for applications in ultrabright superradiant light sources and nonclassical photonic states.

Accelerated radiative decay in confined hBN ensembles leads

Scientists have demonstrated collective emission from ensembles of emitters in hexagonal boron nitride (hBN) layers at room temperature. The research identifies both isolated emitters and ensembles activated by localized electron-beam irradiation using confocal microscopy and a Hanbury Brown-Twiss configuration. Time-resolved photoluminescence measurements revealed a superlinear intensity enhancement and a pronounced acceleration of the radiative decay in tightly confined ensembles, with lifetimes approaching the temporal resolution of the experimental system at approximately 500ps. This represents a significant reduction compared to the 1.85ns observed for single emitters or large, spatially extended ensembles.

Experiments measured a systematic and monotonic acceleration of radiative decay as the number of emitters in an ensemble increased. The team observed lifetimes below 500ps for ensembles, a substantial decrease from the 1.85ns characteristic of individual emitters. Complementary second-order photon-correlation measurements exhibited sub-Poissonian antidips, consistent with emission originating from a few indistinguishable emitters. These measurements confirm the quantum nature of the observed collective emission, indicating coherent behaviour between the emitters. Results demonstrate a direct correlation between lifetime shortening and enhanced emission, providing conclusive evidence of cooperative emission at room temperature without the need for optical cavities or cryogenic cooling.

The study established optically active defect ensembles in hBN as a scalable solid-state platform for engineered collective optics in two-dimensional materials. Scientists estimate the number of emitters within the observed ensembles to be 1, 2, 3, and 4, correlating these numbers with the degree of radiative decay acceleration. The breakthrough delivers a potential pathway towards ultrabright superradiant light sources and nonclassical photonic states for quantum technologies. Measurements confirm that the observed superradiance is not simply a scaling of intensity and lifetime as predicted by the Dicke model, but is influenced by ensemble geometry and emitter dipole orientations. The immediate onset and reproducibility of the lifetime shortening establish these few-emitter defect ensembles as a solid-state, room-temperature realization of collective emission in a two-dimensional material platform, opening new avenues for research and application.

Accelerated Emission From Boron Nitride Emitters

Scientists have demonstrated cooperative spontaneous emission from ensembles of optically active defects in hexagonal boron nitride at room temperature. By identifying small groups of nearly indistinguishable B-center emitters within a sub-wavelength volume, they observed a pronounced acceleration of radiative decay accompanied by enhanced emission intensity. Time-resolved photoluminescence measurements of tightly confined ensembles exhibited significant radiative lifetime shortening, reaching values close to the temporal resolution of the detection system for some ensembles, and photoluminescence enhancement that scaled super-linearly with the number of emitters. Complementary second-order photon-correlation measurements confirmed emission from few B-center emitters and established the cooperative nature of the observed dynamics.

The observed decay acceleration could not be attributed to variations in the local density of optical states or Purcell-type effects, conclusively linking the lifetime reduction to cooperative radiative coupling. These results establish hexagonal boron nitride as a solid-state platform where collective emission emerges robustly under ambient conditions, without requiring optical cavities or cryogenic cooling. The generation of spatially confined defect ensembles using electron-beam irradiation enables access to the crossover between independent and cooperative emission regimes in a two-dimensional material. Authors acknowledge that the bi-exponential model used for the N=4 ensemble suggests the coexistence of collective and non-collective decay channels, representing a limitation in fully characterizing the purely cooperative behaviour. Future research may focus on developing ultrabright and ultrafast quantum light sources operating at room temperature, including defect-based superradiant lasers and electrically driven platforms, building upon this foundational work.