Chinese scientists have unveiled the world's first integrated quantum communication network. The ground portion is made of 700 optical fibers, stretching across 2,000 kilometers (1,200 miles) between Beijing and Shangai. Combined with China’s Quantum Satellite, the full network covers a distance of 4,600 kilometers (2,860 miles). Details of the network are reported in Nature.
Quantum computing holds the promise to revolutionize the world of computers in many ways. A very exciting possibility is the creation of communications that are virtually unhackable. Only users with secure quantum keys will be able to read said messages.
Quantum keys are created by using the quantum states of particles – in this case, photons. These states cannot be guessed or computed, even by the most powerful supercomputer. You either have the particle in that state, or you don’t. And you can’t tap into the conversation either. If you were to “eavesdrop”, you would be changing the particles' properties and it would be obvious the key has been tampered with, without allowing you access.
The other side of the coin is that transmitting these quantum keys is easier said than done, as their quantum properties are easily disrupted. Scientists have worked for several years on how to improve quantum key distribution (QKD). For the ground-based portions, they developed a new technology called Twin-Field QKD which allowed the transmission of keys four times further than previous records.
On the satellite-to-ground part of the network, the tests and improvements conducted over the last few years with the Micius satellite led them to produce a QKD of 47.8 kilobits per second, 40 times faster than their previous record. The team stresses that its channel loss is comparable to what is seen in actual geostationary satellites, so it could be possible in the future for the deployment of quantum satellites in geostationary orbit.
“Our work shows that quantum communication technology is sufficiently mature for large-scale practical applications,” a statement on the study says.
This success shows that a global quantum network with countries building their own and then combine it. China is already planning to expand the network and collaborating with international partners in Austria, Italy, Russia, and Canada. The U.S. is also looking into a national quantum internet network, with the Department of Energy publishing roadmap last July.
The next steps will also include diversifying quantum satellite technology. They plan to construct small and cheap low-earth-orbit satellites, as well as more complex systems to be placed at higher orbits, potentially including geostationary orbit.