Multiwavelength Quantum Correlated Photon Pair Generation for Quantum Entanglement Key Distribution

Abstract

With the rapid advancement of quantum information technology, fully connected multi-user quantum entanglement distribution networks have garnered increasing attention. Among these, multi-wavelength quantum light sources are key devices for establishing connections between multiple users. Despite recent impressive advances, it remains challenging to increase the wavelength number of photon pairs due to limitations in the design and fabrication of nonlinear optical devices. This work explores the potential of silicon nitride (Si<sub>3</sub>N<sub>4</sub>) microring resonators (MRRs) as scalable platforms for multi-wavelength quantum light sources.<br>In this work, we conduct a comprehensive analysis of the key design parameters of the Si<sub>3</sub>N<sub>4</sub> MRRs, including waveguide dimension, resonator dispersion, and coupling condition, to optimize photon-pair generation. Based on these parameters, a Si<sub>3</sub>N<sub>4</sub> MRR with a free spectral range of 20 GHz and an average quality factor of 1.6 million is designed and fabricated. This small free spectral range enables the generation of more channels of correlated photon pairs using the same wavelength resources. The high-quality of the resonator facilitates the high photon pair generation rate, which are critical for quantum entanglement distribution. With a continuous-wave pump laser, correlated photon pairs across a wide spectral range are generated through the spontaneous four-wave mixing (SFWM). The coincidence-to-accidental ratio (CAR) measurements verify the strong quantum correlation between photon pairs, highlighting the reliability of the system for entanglement distribution. Furthermore, the generation and output characteristics of quantum-correlated photon pairs are experimentally investigated with a tunable bandpass filter. The results demonstrate that the successful generation of 71 wavelength-correlated photon pairs within a 25.6 nm spectral range is achieved as shown in the Figure A. Our results pave the way for the development of multi-wavelength quantum light sources with Si<sub>3</sub>N<sub>4</sub> platform, thereby advancing the multi-user quantum networks.