Researchers have for the first time demonstrated the generation of spectrally degenerate twin-photon pairs using a silicon nitride ($\mathrm{Si_3N_4}$) microresonator at telecommunication wavelengths. This advance is significant because, while $\mathrm{Si_3N_4}$ photonic chips were already used as heralded single-photon sources, their ability to produce identical twin photons had not been proven. The technique relies on an inverse four-wave mixing (iFWM) process, where two pump photons with distinct frequencies are converted into a pair of identical twin photons.

The experiment achieved a maximum coincidence-to-accidental ratio (CAR) of $5.4\pm0.6$, a key indicator of the photon source quality. In addition to twin-photon generation, the same microresonator also functioned as a heralded single-photon source via pump-degenerate spontaneous four-wave mixing (SFWM). In this mode, a spectral purity of $P=0.67\pm0.05$ and a heralded anti-bunching of $g^{(2)}_h(0)=0.0042\pm0.0015$ were obtained. These results confirm the versatility of the $\mathrm{Si_3N_4}$ platform for different quantum light generation schemes.

The demonstration of both photon generation schemes on a single integrated $\mathrm{Si_3N_4}$ platform highlights the potential of this material for the development of scalable and tailored quantum light sources. This advance is crucial for applications in quantum communication, quantum computing, and quantum metrology, where the ability to generate photons with controlled properties is fundamental. Integration on silicon nitride chips offers a promising route towards compact and efficient quantum devices.