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arXiv · 2506.21396

Counter-propagating spontaneous parametric down-conversion source in lithium niobate on insulator

Jost Kellner·Alessandra Sabatti·Tristan Kuttner·Robert J. Chapman·Rachel Grange
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Abstract

Quantum photonic technologies rely on the ability to generate, manipulate, and interfere indistinguishable single photons on a scalable platform. Among the various approaches, spontaneous parametric down-conversion (SPDC) remains one of the most widely used methods for generating entangled or pure photon pairs. However most integrated SPDC sources relying on co-propagating geometries have a limited purity of heralded photons, or require lossy filtering. Type-2 SPDC processes can produce pure separable photons but typically suffer from lower efficiency and added complexity due to polarisation management. Here we show the first integrated counter-propagating photon-pair source on lithium niobate on insulator, where signal and idler photons are generated in opposite directions. The counter-propagating geometry leads to spectrally uncorrelated photon pairs without spectral filtering. The joint spectral intensity measurements and unheralded $g^{(2)}$ correlations, yield purities of (92$\pm$3)%. Interference between two independent sources achieves heralded visibilities of (71$\pm$3)%, confirming the scalability of the platform. These results establish a new route toward integrated, high-purity, and tunable photon sources. The demonstrated counter-propagating geometry offers a scalable solution for quantum photonic networks.

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Jost Kellner, Alessandra Sabatti, Tristan Kuttner, Robert J. Chapman, Rachel Grange. 2025-06-26. Counter-propagating spontaneous parametric down-conversion source in lithium niobate on insulator. https://doi.org/10.1364/opticaq.577154

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