Cooperative Emission from Quantum Emitters in Hexagonal Boron Nitride Layers

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.

💡 Research Summary

In this work the authors demonstrate room‑temperature superradiance from few‑emitter ensembles of optically active defects in hexagonal boron nitride (hBN). The study focuses on the so‑called “B‑centers”, carbon‑chain tetramer defects that emit a sharp zero‑phonon line at 436 nm, have homogeneous linewidths narrow enough to be considered nearly indistinguishable, and exhibit radiative lifetimes of about 1.8 ns when isolated. By using localized electron‑beam irradiation, the authors create B‑center ensembles with a controllable number of emitters (N ≈ 1–4) confined within a sub‑wavelength volume (≈50 nm).

Confocal photoluminescence (PL) mapping combined with a Hanbury Brown–Twiss (HBT) setup is employed to characterize both the spatial distribution and the photon statistics of the emitters. Large, spatially extended ensembles generated by prolonged irradiation (high dose) show a mono‑exponential decay with τ ≈ 1.85 ns and a second‑order correlation g²(0)≈1, indicating independent, uncorrelated emission. In contrast, tightly clustered ensembles exhibit a pronounced acceleration of the radiative decay: τ reduces from 1.84 ns for well‑separated emitters to 1.25 ns for a two‑emitter pair, and for N = 3–4 the measured decay approaches the instrumental time resolution of ≈500 ps. Simultaneously, the PL intensity scales super‑linearly with N, approaching the N² dependence expected for ideal Dicke superradiance.

Photon‑correlation measurements reveal a sub‑Poissonian “antibunching antidip” with g²(0)≈0.62 for the two‑emitter case. This value lies between the independent‑emitter lower bound (g²ind(0)=1−1/N) and the ideal superradiant bound (g²>g²ind), confirming partial cooperative behavior. For ensembles with N = 4, a bi‑exponential fit better describes the decay, indicating the coexistence of a fast collective channel and slower non‑collective or dark‑state contributions.

The authors argue that the observed lifetime shortening cannot be attributed to variations in the local density of optical states or Purcell effects, because all emitters reside in the same hBN flake under identical optical conditions. Instead, the reduction is directly linked to coherent dipole‑dipole coupling enabled by sub‑wavelength confinement and spectral indistinguishability.

The study establishes hBN as a solid‑state platform where cooperative spontaneous emission emerges robustly at ambient conditions without the need for optical cavities or cryogenic cooling. The ability to generate deterministic few‑emitter ensembles via electron‑beam patterning opens pathways toward ultrabright, ultrafast quantum light sources, defect‑based superradiant lasers, and the generation of non‑Gaussian quantum states of light. Moreover, the system provides a versatile testbed for exploring many‑body quantum optics, engineered dissipation, and collective quantum states in two‑dimensional materials, with potential applications in quantum communication, sensing, and integrated quantum photonics.