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arXiv · 2506.07029

Inline Quantum Measurements with SNSPDs Coupled to Photonic Bound States

Filippo Martinelli·Anton N. Vetlugin·Shuyu Dong·Darren M. Z. Koh·Mariia Sidorova·Christian Kurtsiefer·Cesare Soci
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Abstract

We report the realization of inline quantum measurements with waveguide-integrated superconducting nanowire single-photon detectors (SNSPDs). To suppress parasitic scattering at detector terminations, while ensuring compatibility with standard photonic substrates and cryogenic operation, we developed a photonic bound states in the continuum (BIC) platform based on etchless polymer waveguides. We show BIC-coupled inline detectors with on-chip efficiency exceeding 80%, recovery time of less than 2 ns, and intrinsic jitter of less than 70 ps. As a proof of principle, we implement Hanbury Brown and Twiss interferometry and photon number resolution with two collinear detectors within a footprint of $60 \cdot 6$ $\mu m^2$. The concept of inline quantum measurements could be further developed to support more complex circuit functionalities, such as higher-order correlation measurements, quantum state tomography, and multi-photon subtraction, within a compact architecture.

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Filippo Martinelli, Anton N. Vetlugin, Shuyu Dong, Darren M. Z. Koh, Mariia Sidorova, Christian Kurtsiefer, Cesare Soci. 2025-06-08. Inline Quantum Measurements with SNSPDs Coupled to Photonic Bound States. https://arxiv.org/abs/2506.07029

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