China to complete first stretch of dedicated 'quantum' encryption fibre network next month

2,000km network to provide foundation for secure quantum key distribution

China is building a ‘quantum' network between four of its major cities in order to provide secure communications for government and defence that is untappable by foreign intelligence services.

The fibre cabling, connecting the capital Beijing with Shanghai, on the coast, will be completed by the end of the year and will comprise 32 trusted nodes. The 2,000km network is routed via Jinan and Hefei on the east of China. The project is being led by researchers from the University of Science and Technology of China.

The network is primarily intended for the exchange of quantum keys for secure communication, although one potential weakness in the network lies at each node where quantum keys will need to be converted into standard information in order to either decrypt or route accordingly.

The construction of the quantum network - a world first - coincides with the launch of a satellite by China dedicated to researching the distribution of quantum keys over long distances.

According to Tim Spiller, director of the UK's own Quantum Communications Hub, quantum key distribution is limited by distance because it encodes information in the states of individual photons. Over fibre or transmitted through the air, the photons become absorbed or scattered, he says.

Quantum key distribution over long distances therefore requires what's called quantum entanglement, "a property that can link the states of photons separated by great physical distance and that can be exchanged between photons", according to the Institute of Electrical and Electronics Engineers (IEEE).

The construction of the network, which is part research and part practical, comes at a time of heightened interest in quantum computing, with some research moving out of institutes and universities into companies like Google and start-ups such as D-Wave. The UK government has also invested substantial sums in research into quantum computing.

However, some researchers claim that quantum cryptography also comes with a variety of flaws.