Laneve Alessandro, Rota Michele B, Basso Basset Francesco, Beccaceci Mattia, Villari Valerio, Oberleitner Thomas, Reum Yorick, Krieger Tobias M, Buchinger Quirin, Prasad Rohit, da Silva Saimon F Covre, Pfenning Andreas, Stroj Sandra, Höfling Sven, Rastelli Armando, Huber-Loyola Tobias, Trotta Rinaldo
Dipartimento di Fisica, Sapienza Università di Roma, Piazzale Aldo Moro 5, Roma, Italy.
Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, Milano, Italy.
Nat Commun. 2025 Jul 5;16(1):6209. doi: 10.1038/s41467-025-61460-3.
The generation of entangled photons from radiative cascades has enabled milestone experiments in quantum information science with several applications in photonic quantum technologies. Significant efforts are being devoted to pushing the performances of near-deterministic entangled-photon sources based on single quantum emitters often embedded in photonic cavities, so to boost the flux of photon pairs. The general postulate is that the emitter generates photons in a nearly maximally entangled state of polarization, ready for application purposes. Here, we demonstrate that this assumption is unjustified. We show that in radiative cascades there exists an interplay between photon polarization and emission wavevector, which can be further amplified by embedding the emitters in micro-cavities. We discuss how the polarization entanglement of photon pairs from a biexciton-exciton cascade in quantum dots strongly depends on their propagation wavevector and we even observe entanglement vanishing for large emission angles. Our experimental results, backed by theoretical modeling, yield a brand-new understanding of cascaded emission for various quantum emitters. In addition, our model provides quantitative guidelines for designing optical microcavities that retain both a high degree of entanglement and collection efficiency, moving the community one step further towards an ideal source of entangled photons for quantum technologies.
通过辐射级联产生纠缠光子，使得量子信息科学领域取得了具有里程碑意义的实验成果，并在光子量子技术中得到了多种应用。目前人们正在付出巨大努力，致力于提升基于通常嵌入光子腔中的单量子发射器的近确定性纠缠光子源的性能，以提高光子对的通量。一般的假设是，发射器会产生处于几乎最大纠缠偏振态的光子，可供应用。在此，我们证明这一假设是不合理的。我们表明，在辐射级联中，光子偏振和发射波矢之间存在相互作用，将发射器嵌入微腔中可进一步放大这种相互作用。我们讨论了量子点中双激子 - 激子级联产生的光子对的偏振纠缠如何强烈依赖于它们的传播波矢，甚至观察到在大发射角时纠缠消失。我们的实验结果在理论建模的支持下，对各种量子发射器的级联发射产生了全新的理解。此外，我们的模型为设计既能保持高度纠缠又能保持收集效率的光学微腔提供了定量指导方针，使该领域朝着量子技术的理想纠缠光子源又迈进了一步。
