  With the advance development in quantum science, constructing a large-scale
quantum network has become a hot area of future quantum information technology.
Future quantum networks promise to enable many fantastic applications and will
unlock fundamentally new technologies in information security and large-scale
computation. The future quantum internet is required to connect quantum
information processors to achieve unparalleled capabilities in secret
communication and enable quantum communication between any two points on Earth.
However, the existing quantum networks are basically constructed to realize the
communication between the end users in their own networks. How to bridge
different independent networks to form a fully-connected quantum internet
becomes a pressing challenge for future networks. Here, we demonstrate the
quantum fusion of two independent networks for the first time based on
multiuser entanglement swapping, to merge two 10-user networks into a larger
network with 18 users in quantum correlation layer. By performing the Bell
state measurement between two nonneighboring nodes, the users from different
networks can establish entanglement and ultimately every pair of the 18 users
are able to communicate with each other using the swapped states. Our approach
opens attractive opportunities for the establishment of quantum entanglement
between remote nodes in different networks, which facilitates versatile quantum
information interconnects and has great application in constructing large-scale
intercity quantum communication networks.
