Coexistence of multiuser entanglement distribution and classical light in optical fiber network with a semiconductor chip

Abstract

Building communication links among multiple users in a scalable and robust way is a key objective in achieving large-scale quantum networks. In a realistic scenario, noise from the coexisting classical light is inevitable and can ultimately disrupt the entanglement. The previous significant fully connected multiuser entanglement distribution experiments are conducted using dark fiber links, and there is no explicit relation between the entanglement degradations induced by classical noise and its error rate. Here, a semiconductor chip with a high figure-of-merit modal overlap is fabricated to directly generate broadband polarization entanglement. The monolithic source maintains the polarization entanglement fidelity of above 96% for 42 nm bandwidth, with a brightness of 1.2 × 10⁷ Hz mW⁻¹. A continuously working quantum entanglement distribution are performed among three users coexisting with classical light. Under finite-key analysis, secure keys are established and images encryption are enabled as well as quantum secret sharing between users. This work paves the way for practical multiparty quantum communication with integrated photonic architecture compatible with real-world fiber optical communication network.