Recently, our research team made a major breakthrough in quantum communication technology. We have innovatively proposed and realized a new paradigm for constructing fully connected quantum communication networks based on active temporal and wavelength multiplexing. By combining this novel approach with highly efficient chirped-polarization lithium niobate (LN) photonic chips, we demonstrated the first experimental realization of quantum fusion between two independent networks through multi-user entanglement swapping. This resulted in a fully connected topological quantum communication network, providing a crucial foundation for future quantum internet construction. This work has been published in the top-tier international journal Nature Photonics under the title “Quantum Fusion of Independent Networks via Multi-User Entanglement Swapping.”

Quantum information technology inherently transcends the limitations of classical information technology, establishing it as one of the most strategic frontiers in contemporary technological innovation. The quantum no-cloning theorem endows quantum cryptography with theoretically unconditional security, while quantum computing, leveraging quantum superposition, offers exponential speedups for specific problems, surpassing the capabilities of classical computers. Analogous to the internet's role in converging and advancing modern information and computer science, a future quantum internet will serve as a critical infrastructure for key quantum technologies—such as quantum communication, computing, and sensing—significantly accelerating scientific and technological progress and enabling applications that fundamentally disrupt classical paradigms.

In recent years, fully connected quantum communication networks have attracted considerable interest for enabling simultaneous multi-user communication with minimal infrastructure and hardware requirements. As a key architecture for realizing a fully connected quantum internet, this approach holds potential to revolutionize future information exchange. Current quantum networks, however, primarily facilitate intra-domain communication (Conceptual Diagram a). Achieving coherent fusion among independent multi-user quantum networks is therefore crucial for advancing the future quantum internet. Consequently, bridging disparate independent networks into a fully interconnected quantum internet represents one of the most pressing challenges in quantum networking. This effort faces two major hurdles: establishing a fully connected topological structure among independent networks (Conceptual Diagrams b-d), and achieving simultaneous high-quality entanglement swapping across all involved entangled states.

Conceptual diagram of independent quantum network fusion.

(a) Active temporal and wavelength multiplexing scheme

In this work, we address key challenges in quantum fusion by pioneering an active time-wavelength multiplexing scheme (Conceptual Diagrams e-f) to establish a new quantum communication network paradigm. Within this scheme, each user receives a single wavelength channel containing N-1 temporally independent photon groups, where each group is entangled with one of the other N-1 users. Our quantum processor generates entangled photon pairs via spontaneous parametric down-conversion (SPDC) using 2N-3 custom-designed pump pulses with specific wavelength and temporal profiles, distributing them to end-users through the quantum channel. To ensure efficient entangled-pair generation across all pump lasers, we leverage the quasi-phase-matched low-dispersion characteristics of LN, fabricating chirped-poled thin-film LN photonic chips to enable broadband nonlinear second-harmonic generation and SPDC. For efficient discrimination of photon pairs, a time-division multiplexing scheme isolates distinct pump pulses, enabling users to identify entangled states based on photon arrival times. All symmetric wavelength channels share different entangled states, establishing a fully connected network topology.

(b) Quantum network fusion based on multi-user entanglement swapping

In the verification experiment, we constructed two 10-user quantum networks and performed multi-user entanglement swapping via an active time-wavelength multiplexing scheme. Polarization entanglement measurements yielded interference fringe visibilities exceeding 95% per state, with the average quantum state fidelity of post-swapping entanglement reaching 84.5%. Through multi-user entanglement swapping, the two independent networks merged at the quantum correlation layer, forming a larger fully connected quantum network with 18 endpoints. Each endpoint utilized a single wavelength channel, enabling quantum state discrimination based on photon arrival time. By precisely synchronizing pump pulse delays between networks, corresponding signals were overlapped to facilitate entanglement swapping between any two users across different networks. Consequently, all end-users achieved inter-network communication via entanglement-based quantum key distribution protocols. This approach successfully realizes the fusion and interconnection of heterogeneous quantum networks, demonstrating significant potential for scalable quantum internet construction.

Results of fully connected quantum network constructed using active temporal and wavelength multiplexing。

This study introduces an innovative active temporal-wavelength multiplexing scheme, establishing a scalable framework for constructing high-performance, large-scale quantum networks with fully connected topologies. The resulting fully connected quantum communication network enables arbitrary user-to-user communication while minimizing deployment infrastructure requirements, positioning it as a key architecture candidate for the future quantum internet. As practical quantum technologies like quantum repeaters mature, a global quantum internet is poised to become a reality in the foreseeable future.

This work is published in “Yiwen Huang, Yilin Yang, Hao Li, Jiayu Wang, Jing Qiu, Zhantong Qi, Yuting Zhang, Yuanhua Li, Yuanlin Zheng and Xianfeng Chen, Quantum fusion of independent networks based on multi-user entanglement swapping, Nature Photoncis, 1-9 (2025)”.

Link: https://www.nature.com/articles/s41566-025-01792-0