Advancements in Quantum Networking: Two Networks Successfully Fuse

Researchers at Shanghai Jiao Tong University have successfully fused two independent quantum networks, marking a significant milestone in quantum networking and inching closer to a global quantum internet.

This groundbreaking achievement allows 18 users to communicate securely using entanglement-based protocols, a feat that demonstrates the complexity and potential of multi-user quantum networks. Previous attempts at connecting quantum computers within the same network have been successful, but linking multiple users across different networks has been a considerable challenge.

The method employed for this fusion is known as multi-user entanglement swapping. This process begins with two separate networks, each composed of 10 nodes that are already entangled with one another but not with nodes in the other network.

By using one node from each network to merge them, the researchers effectively formed an 18-user network where all nodes are connected. According to the study published in Nature Photonics, Bell state measurements were crucial in linking the two networks, although this measurement causes the wave functions of the measured photons to collapse, resulting in 18 usable nodes instead of 20.

The researchers also introduced an active temporal and wavelength multiplexing scheme, diverging from previous dense wavelength division multiplexing methods, to enhance their experimental setup and improve entanglement quality.

Their findings revealed high-quality entanglement with fidelity measurements exceeding 84% and interference visibilities ranging from 75% to 90.7%, compared to only 50% in classical systems. However, despite this progress, the study highlights that scaling these networks for larger and longer distances poses significant challenges.

The most pressing issue is the development of quantum repeaters, which are essential for transmitting signals over longer distances without losing crucial photons. The team noted that while advancements in quantum memory have been made, establishing robust entanglement between remote quantum memory nodes remains a critical hurdle for practical long-distance quantum communication networks.

The authors expressed optimism about their work, stating that their approach paves the way for establishing quantum entanglement among remote nodes across different networks. This could facilitate the construction of large-scale intercity quantum communication networks, marking a transformative step in secure communications.