Twin-photon generation in a silicon nitride microresonator

Abstract

Photonic chips with silicon nitride ($\mathrm{S}{\mathrm{i}}_3{\mathrm{N}}_4$) microring resonators are well established as heralded single-photon sources, but their operation as frequency-degenerate twin-photon sources has not previously been demonstrated. Here, we realise a twin-photon source at telecommunication wavelengths in a $\mathrm{S}{\mathrm{i}}_3{\mathrm{N}}_4$ ring microresonator via an inverse four-wave mixing (FWM) process, in which two photons from spectrally distinct pumps are converted into a pair of identical twin photons. The measurements show a maximum coincidence-to-accidental ratio (CAR) of $5.4\pm 0.6$. In addition, the microresonator functions as a heralded single-photon source through pump-degenerate spontaneous four-wave mixing (SFWM), exhibiting a spectral purity of $P=0.67\pm 0.05$ and a heralded anti-bunching of $g_h^{(2)}(0)=0.0042\pm 0.0015$. Together, these results demonstrate both photon-generation schemes on a single integrated $\mathrm{S}{\mathrm{i}}_3{\mathrm{N}}_4$ platform, highlighting its potential for scalable, tailored quantum light generation.