Free-standing circular Bragg gratings enabling efficient GaAs quantum dot entangled photon pair sources

Sai Abhishikth Dhurjati; Moritz Langer; Yared G. Zena; Ahmad Rahimi; Liesa Raith; Martin Bauer; Frank H. P. Fitzek; Riccardo Bassoli; Caspar Hopfmann

arXiv · 2605.02360

Free-standing circular Bragg gratings enabling efficient GaAs quantum dot entangled photon pair sources

Sai Abhishikth Dhurjati·Moritz Langer·Yared G. Zena·Ahmad Rahimi·Liesa Raith·Martin Bauer·Frank H. P. Fitzek·Riccardo Bassoli·Caspar Hopfmann

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Abstract

Deterministic and bright quantum light sources based on scalable semiconductor technologies are a crucial building block for future quantum communication networks. While circular Bragg gratings (CBGs) are highly effective for extracting light from solid-state quantum emitters, conventional architectures rely on complex multi-layer processing or flip-chip bonding, which introduce detrimental strain and limit scalability. Here, we present a fabrication-minimal approach to realize monolithic, free-standing CBG cavities with deterministically positioned single GaAs quantum dots (QDs). By utilizing aspect-ratio-dependent etching (ARDE) in a single-step top-down process, we achieve the necessary vertical structural asymmetry for directional emission without requiring bottom reflectors. Finite-difference time-domain (FDTD) simulations validate this geometry, predicting free-space extraction efficiencies up to $68 \, \%$ and coupling efficiencies of $40 \, \%$ into a lensed single-mode fiber ($\text{NA} = 0.6$). Experimentally, the deterministically coupled QD-CBG devices yield a photoluminescence intensity enhancement of up to $\times 700$ compared to unprocessed planar QDs, reaching integrated count rates of $45 \, MHz$. Furthermore, the suspended membrane architecture effectively relaxes residual strain, significantly reducing the average exciton fine-structure splitting from $7.3 \, \mu eV$ in planar QDs to $1.3 \, \mu eV$ in the CBGs. Interferometric measurements confirm that the fabrication process preserves the optical quality of the emitters, with average coherence times of $70 \, ps$. By bridging optimized FDTD design with precise nanofabrication and robust optical performance, these results establish free-standing GaAs CBGs as a highly scalable platform for bright and coherent entangled photon pair sources.

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Sai Abhishikth Dhurjati, Moritz Langer, Yared G. Zena, Ahmad Rahimi, Liesa Raith, Martin Bauer, Frank H. P. Fitzek, Riccardo Bassoli, Caspar Hopfmann. 2026-05-04. Free-standing circular Bragg gratings enabling efficient GaAs quantum dot entangled photon pair sources. https://arxiv.org/abs/2605.02360

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