In-Line Fiber-Integrated Photon-Pair Generation from van der Waals Crystals

Quantum Physics [Submitted on 25 Mar 2026] In-Line Fiber-Integrated Photon-Pair Generation from van der Waals Crystals Mayank Joshi, Tanumoy Pramanik, Mengting Jiang, Yu Xing, Zhaogang Dong, Yuerui Lu, Jie Zhao, Ping Koy Lam, Syed M. Assad, Xuezhi Ma, In Cheol Seo, Young-Wook Cho Miniaturized quantum light sources that operate directly in optical fibers are an attractive platform for optical quantum technologies. However, most miniaturized spontaneous parametric down- conversion (SPDC) sources still rely on objective-lens-based free-space pumping and collection, which limits compactness, robustness, and direct compatibility with fiber-based systems. Here we demonstrate a lens-free in-line SPDC photon-pair source by integrating a van der Waals NbOI2 flake directly onto the end facet of an optical fiber. In this configuration, the generated photon- pairs are efficiently collected into optical fibers, eliminating the need for bulk free-space collection optics. Despite the limited numerical aperture of the single-mode fiber, efficient photon-pair collection with high purity, characterized by a coincidence-to-accidental ratio of up to ~4600, is achieved in an ultracompact configuration. These results establish van der Waals ferroelectric materials as a promising platform for fiber-integrated quantum light sources and provide a pathway toward compact, alignment-free quantum photonic devices. Subjects: Quantum Physics (quant-ph) Cite as: arXiv:2603.24070 [quant-ph]   (or arXiv:2603.24070v1 [quant-ph] for this version)   https://doi.org/10.48550/arXiv.2603.24070 Focus to learn more Submission history From: Mayank Joshi [view email] [v1] Wed, 25 Mar 2026 08:24:49 UTC (3,660 KB) Access Paper: HTML (experimental) view license Current browse context: quant-ph < prev   |   next > new | recent | 2026-03 References & Citations INSPIRE HEP NASA ADS Google Scholar Semantic Scholar Export BibTeX Citation Bookmark Bibliographic Tools Bibliographic and Citation Tools Bibliographic Explorer Toggle Bibliographic Explorer (What is the Explorer?) Connected Papers Toggle Connected Papers (What is Connected Papers?) Litmaps Toggle Litmaps (What is Litmaps?) scite.ai Toggle scite Smart Citations (What are Smart Citations?) Code, Data, Media Demos Related Papers About arXivLabs Which authors of this paper are endorsers? | Disable MathJax (What is MathJax?)