Researchers at Shanghai Jiao Tong University have achieved a significant milestone in quantum communications by successfully merging two independent quantum networks. This breakthrough, reported on November 5, 2025, represents a critical step toward realizing a global quantum internet, where users can conduct secure communications and large-scale quantum computing through quantum entanglement.
The merging of these networks marks the most complex multi-user quantum network to date, consisting of 18 users who can now communicate securely using entanglement-based protocols. Achieving this level of connectivity is particularly challenging, as interconnecting quantum networks is more difficult than linking classical networks. While previous research has demonstrated connections within single networks, the fusion of multiple users across distinct networks has remained a formidable hurdle.
Innovative Methods for Network Integration
To facilitate this two-system fusion, the researchers employed a technique known as “multi-user entanglement swapping.” This process starts with two separate networks, each containing 10 nodes that are entangled with one another but not with nodes from the other network. By using one node from each network to connect them, the researchers effectively merged the two networks while allowing the remaining 18 nodes to communicate with each other.
The process relies on Bell state measurements to link the two networks. These measurements yield entanglement but also collapse the wave functions of the measured photons, which is why only 18 out of the original 20 nodes can participate after the entanglement swapping. As the study’s authors explain, “Ultimately, the two 10-user fully connected networks are merged into an 18-user network in the quantum correlation layer after the multi-user entanglement swapping.”
Additionally, the team developed an active temporal and wavelength multiplexing (ATWM) scheme, diverging from the dense wavelength division multiplexing (DWDM) used in prior studies. Their results confirmed high-quality entanglement, achieving fidelities above 84% and interference visibilities ranging from 75% to 90.7%. In contrast, classical systems typically operate at around 50% fidelity.
Future Challenges and Opportunities
While merging independent networks is a significant achievement, the path to larger and longer-distance quantum networks remains fraught with challenges. A key obstacle is the development of quantum repeaters, which are necessary for maintaining signal integrity over greater distances. The authors of the study highlight that “the most critical challenge in realizing practical long-distance quantum repeater networks is the establishment of robust entanglement between remote quantum memory nodes.”
Despite these hurdles, the research team expresses optimism about their findings. They assert that their work “opens attractive opportunities for the establishment of quantum entanglement between remote nodes in different networks,” paving the way for versatile quantum information interconnections. This advancement could have significant implications for the construction of large-scale intercity quantum communication networks.
As the scientific community continues to explore the potential of quantum technologies, this study adds a promising chapter to the ongoing efforts to create a global quantum internet. The implications of such a network could transform secure communications and computational capabilities worldwide, underscoring the importance of continued research and innovation in this field.
