Cooperative Emission from Quantum Emitters in Hexagonal Boron Nitride Layers

Abstract

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.

Figures (3)

• Figure 1: Large and uncorrelated ensemble of quantum emitters. (a) Schematic of the photoluminescence (PL) measurement from hBN optical active defects in a Hanbury Brown–Twiss (HBT) configuration. (b) SEM image of the hBN flake after a strong localized irradiation, showing an activated defect site (black spot; irradiation time $\sim 15$ min). (c) wide-field confocal PL scan identifying an irradiated region as a defect ensemble. (d) Zoom-in confocal PL map revealing the quantum-emitter ensembles. (e) Normalized second-order photon correlation $g^{(2)}(\tau)$ for the ensemble, showing $g^{(2)}(0) \approx 1$ corresponding to uncorrelated ensemble of quantum emitters. (f) Time-resolved PL traces for the typical large and uncorrelated ensemble, showing mono-exponential lifetimes of $1.85$ ns.
• Figure 2: Separated versus spatially localized emitters: non-cooperative and superradiant regimes. (a) SEM image of the hBN flake after multiple localized irradiations, showing activated defect sites (black spots; irradiation times 5--300 s). (b) wide-field PL scan identifying each irradiated spot as a defect ensemble. Conceptual comparison of emitters placed far apart (c), resulting in non-cooperative emission, versus (d) two emitters positioned within a sub-wavelength distance, enabling cooperative emission. Confocal PL map showing the spatial arrangement of the emitters. (e) Second-order photon-correlation measurement revealing a subpossonian bunching antidip of $g^{(2)}(0)\approx 0.62$, consistent with a two-emitter ensemble. (f) Time-resolved PL traces showing an accelerated decay of $1.25\,\text{ns}$ for the tightly spaced (superradiant) emitters compared to $1.84\,\text{ns}$ for the spatially separated (non-superradiant) emitters.
• Figure 3: Superradiant scaling with ensemble size. (a,b) Two-dimensional PL maps of a tightly confined emitter ensemble within a diffraction-limited area, exhibiting a pronounced super-linear enhancement of the PL intensity. (c) Non-normalized time-resolved PL traces recorded under identical excitation and detection conditions for ensembles containing a lower-bound estimate of $N=1$, $2$, $3$ and $4$ emitters. The inset shows the extracted peak PL amplitude and radiative lifetime $\tau$, obtained from mono-exponential fits, as a function of $N$. For $N=4$, the decay is better described by a bi-exponential fit, and the fast component is used to extract the effective radiative lifetime. Uncertainties in extracted values of $\tau$ do not exceed 20ps. Ensembles with higher estimated number of emitters exhibit pronounced lifetimes shortening that approach and fall below the temporal resolution of the measurement system (500ps). Black curves are shown to demonstrate the trend.