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

TL;DR

This paper demonstrates a scalable multiuser quantum entanglement distribution system coexisting with classical light in optical fibers, using a semiconductor chip source that maintains high fidelity and enables secure quantum communication.

Contribution

It introduces a monolithic semiconductor chip source for broadband polarization entanglement and shows its effective coexistence with classical light in fiber networks for multiuser quantum communication.

Findings

High-fidelity polarization entanglement (>96%) over 42 nm bandwidth.

Successful multiuser entanglement distribution with classical light coexistence.

Secure keys and quantum secret sharing achieved in fiber networks.

Abstract

Building communication links among multiple users in a scalable and robust way is a key objective in achieving large-scale quantum networks. In 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 we fabricate a semiconductor chip with a high figure-of-merit modal overlap to directly generate broadband polarization entanglement. Our monolithic source maintains polarization entanglement fidelity above 96% for 42 nm bandwidth with a brightness of 1.2*10^7 Hz/mW. We perform a continuously working quantum entanglement distribution among three users coexisting with classical light. Under finite-key analysis, we establish secure keys and enable images encryption as well as quantum secret sharing between users. Our work paves the way for practical multiparty quantum communication with integrated photonic architecture compatible with real-world fiber optical communication network.