Down-converted photon pairs in a high-Q silicon nitride microresonator

Bohan Li, Zhiquan Yuan, James Williams, Warren Jin, Adrian Beckert, Tian Xie, Joel Guo, Avi Feshali, Mario Paniccia, Andrei Faraon, John Bowers, Alireza Marandi and Kerry Vahala ()
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Bohan Li: California Institute of Technology
Zhiquan Yuan: California Institute of Technology
James Williams: California Institute of Technology
Warren Jin: Anello Photonics
Adrian Beckert: California Institute of Technology
Tian Xie: California Institute of Technology
Joel Guo: University of California Santa Barbara
Avi Feshali: Anello Photonics
Mario Paniccia: Anello Photonics
Andrei Faraon: California Institute of Technology
John Bowers: University of California Santa Barbara
Alireza Marandi: California Institute of Technology
Kerry Vahala: California Institute of Technology

Nature, 2025, vol. 639, issue 8056, 922-927

Abstract: Abstract Entangled photon pairs from spontaneous parametric down-conversion (SPDC)1 are central to many quantum applications2–6. SPDC is typically performed in non-centrosymmetric systems7 with an inherent second-order nonlinearity (χ(2))8–10. We demonstrate strong narrowband SPDC with an on-chip rate of 0.8 million pairs per second in Si3N4. Si3N4 is the pre-eminent material for photonic integration and also exhibits the lowest waveguide loss (which is essential for integrated quantum circuits). However, being amorphous, silicon nitride lacks an intrinsic χ(2), which limits its role in photonic quantum devices. We enabled SPDC in Si3N4 by combining strong light-field enhancement inside a high optical Q-factor microcavity with an optically induced space-charge field. We present narrowband photon pairs with a high spectral brightness. The quantum nature of the down-converted photon pairs is verified through coincidence measurements. This light source, based on Si3N4 integrated photonics technology, unlocks new avenues for quantum systems on a chip.

Date: 2025
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DOI: 10.1038/s41586-025-08662-3

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