Down-converted photon pairs in a high-Q silicon nitride microresonator.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 40108472.
- Also identified by DOI 10.1038/s41586-025-08662-3 and PMC identifier 11946901.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
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.