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Spectrally Robust Photon-Pair Generation in Topological Waveguide Arrays

A. Zecchetto1, J.-R. Coudevylle2, M. Morassi2, A. Lemaître2, M. I. Amanti1, S. Ducci1, and F. Baboux1,3,*

  • *Contact author: florent.baboux@u-paris.fr
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PRX Quantum 7, 043030 – Published 12 November, 2026

DOI: https://doi.org/10.1103/kszt-p63d

Abstract

Harnessing topological effects offers a route to protect quantum states of light from imperfections, potentially enabling more robust platforms for quantum information processing. This capability is particularly relevant for active photonic circuits that generate quantum light directly on-chip. However, the impact of topology on the spectral properties of parametric processes—crucial for scalable quantum photonic circuits—remains largely unexplored. Here, we address this question by investigating photon-pair generation via spontaneous parametric down-conversion (SPDC) in nonlinear waveguide arrays, combining experiment and theory. A systematic comparison of uniform, trivial, and topological Su-Schrieffer-Heeger (SSH) arrays reveals that only the topological configuration preserves a stable SPDC resonance spectrum under coupling disorder, with fluctuations in the resonance wavelength reduced by more than an order of magnitude. An analytical model captures the origin of this robustness in the band-structure properties of the interacting modes. Numerical analysis further shows that each SSH array can operate as a robust photon-pair source, enabling stable interference between multiple such sources and the generation of high-dimensional entangled states with high fidelity. These results establish nonlinear waveguide arrays as a promising platform for harnessing the interplay of topology and nonlinearity in quantum photonic circuits.

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The integration of many sources of quantum light on a single chip is an important step toward scaling up quantum photonic technologies. For these sources to interfere properly, they must emit photons with nearly identical spectral properties. However, small fabrication imperfections inevitably introduce variations from one device to another, shifting their spectra and degrading quantum interference. Because topological photonic systems can remain robust against certain forms of disorder, we investigate here whether this robustness can also stabilize the spectral properties of photon-pair generation. By combining experiments on spontaneous parametric down-conversion in nonlinear waveguide arrays with theory and numerical simulations, we compare conventional and topological designs. We find that topological Su-Schrieffer-Heeger arrays maintain a highly stable resonance spectrum even in the presence of substantial coupling disorder, with resonance-wavelength fluctuations reduced by more than an order of magnitude. Our simulations further show that this stability extends to the spectral properties of the emitted photon pairs, enabling high-quality interference between multiple photon-pair sources. These results show how topology can improve the spectral uniformity of integrated quantum-light sources and reduce their sensitivity to fabrication imperfections, supporting the development of larger quantum photonic circuits. They also establish nonlinear waveguide arrays as a promising platform for exploring the rich interplay between topology, disorder, and nonlinearity in the quantum regime.

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PRX Quantum 7, 043030– Published 12 November, 2026
  • Received 23 March 2026
  • Revised 17 July 2026
  • Accepted 17 September 2026
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