Down-converted photon pairs in a high-Q silicon nitride microresonator
Entangled photon pairs from spontaneous parametric down-conversion (SPDC)<sup>1</sup> are central to many quantum applications<sup>2-6</sup>. SPDC is typically performed in non-centrosymmetric systems<sup>7</sup> with an inherent second-order nonlinearity (χ<sup>(2)</sup>)<sup>8-10</sup>. We demonstrate strong narrowband SPDC with an on-chip rate of 0.8 million pairs per second in Si<sub>3</sub>N<sub>4</sub>. Si<sub>3</sub>N<sub>4</sub> 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<sup>(2)</sup>, which limits its role in photonic quantum devices. We enabled SPDC in Si<sub>3</sub>N<sub>4</sub> 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 Si<sub>3</sub>N<sub>4</sub> integrated photonics technology, unlocks new avenues for quantum systems on a chip.
Authors
- Alireza Marandi (ORCID: https://orcid.org/0000-0002-0470-0050)
- Kerry J. Vahala (ORCID: https://orcid.org/0000-0003-1783-1380)
- Joel Guo (ORCID: https://orcid.org/0000-0003-0203-5170)
- Warren Jin (ORCID: https://orcid.org/0000-0002-4297-7982)
- Mario Paniccia (ORCID: https://orcid.org/0009-0009-5006-3871)
- Tian Xie (ORCID: https://orcid.org/0000-0003-0917-3592)
- Adrian Beckert (ORCID: https://orcid.org/0000-0001-7218-4214)
- Andrei Faraon (ORCID: https://orcid.org/0000-0002-8141-391X)
- Zhiquan Yuan (ORCID: https://orcid.org/0000-0001-9054-6004)
- James Williams (ORCID: https://orcid.org/0000-0001-9073-5745)
- Avi Feshali (ORCID: https://orcid.org/0000-0002-6991-8392)
- Bohan Li (ORCID: https://orcid.org/0009-0007-8210-1903)
- John E. Bowers (ORCID: https://orcid.org/0000-0003-4270-8296)
Institutions
- California Institute of Technology (US)
- University of California, Santa Barbara (US)
Publication Details
- Journal
- Nature
- Published
- 2025-03-19
- DOI
- https://doi.org/10.1038/s41586-025-08662-3
- Citations
- 28
- Primary Topic
- Advanced Fiber Laser Technologies
- Type
- article
- Field-Weighted Citation Impact
- 34.91
Funders
- California Institute of Technology
- University of California, Santa Barbara
- Advanced Research Projects Agency
- Kavli Nanoscience Institute, California Institute of Technology