Silicon Nitride Quantum Emitters for Room-Temperature Quantum Key Distribution

Intrinsic single-photon emitters in silicon nitride (SiN) have sparked considerable interest in the field of integrated quantum photonics due to their exceptional single-photon purity at room temperature and the potential for seamless integration into technologically mature SiN photonic devices. In this work, we focus on developing highly efficient single-photon sources within the SiN platform that exhibit high single-photon purity, brightness, stability, and polarization properties for applications in quantum key distribution (QKD) protocols. We applied a solid-immersion lens (SIL) approach to demonstrate ultra-bright SiN quantum emitters. We realized emitters with a saturated single-photon emission rate of on the order of MHz and, at the same time, single-photon purity quantified by second-order autocorrelation measurements yielding a g⁽²⁾(0) value of 0.07. Additionally, we explore the possibility of quantum frequency conversion using on-chip SiN ring resonators to transform photons into the telecom range, which is crucial for long-distance communication. As an ultimate goal, we aim to implement an experimental testbed for room-temperature QKD with SiN quantum emitters and validate their performance.