The project leader Siddarth K Joshi optimising the central quantum network hub.

Quantum network demonstrated by Quantum Communications Hub investigators is largest of its kind

The quantum internet is one step closer to becoming reality, thanks to the work of Quantum Communications Hub investigators and their collaborators, who have demonstrated the largest ‘fully connected quantum network’, to date.

Given the serious cybersecurity threats imposed by major advances in quantum computing and increasingly advanced hackers, there is a growing need to incorporate new security technologies into networks, which are integral to much of our communications infrastructure.  Quantum networks are far more secure than conventional networks as they rely on the fundamental properties of quantum physics, as opposed to complex codes which are difficult to crack, to provide security. 

Quantum networks can be classified into one of three categories: trusted node networks, where the nodes within the network are assumed to be safe from eavesdroppers; access networks, where only certain pairs of users are allowed to exchange a key at a time; and fully connected quantum networks, where every user is connected to every other user directly. The network, demonstrated by the team led by Dr Siddarth Joshi from QET Labs Bristol, is an example of a fully connected network and uses the existing fibre optic network within the city of Bristol. The demonstration enabled simultaneous and secure connections between 28 pairings of eight users, making it largest in the world in terms of number of users. 

Until now, fully connected quantum networks have posed scalability problems, however the team have overcome this by using a method called multiplexing entanglement. Entanglement is the property that gives correlations between two or more quantum systems, even when these are separated by large distances, meaning if the state of one system is measured, the state of the other is automatically known. This can be used to generate encryption keys to secure data. Multiplexing entanglement enables light particles, produced by a single system, to be split so they can be received by several users, massively increasing efficiency of the network. The revolutionary methods used could potentially enable the network to serve millions of users in the future, according to Joshi.

Speaking about the major advancement, lead author, Joshi, said:

“This represents a massive breakthrough and makes the quantum internet a much more realistic proposition. Until now, building a quantum network has entailed huge cost, time, and resource, as well as often compromising on its security which defeats the whole purpose.”

“Our solution is scalable, relatively cheap and, most important of all, impregnable. That means it’s an exciting game changer and paves the way for much more rapid development and widespread rollout of this technology.”

A quantum network that can support all forms of quantum communications technologies will be required for the quantum internet to be effective in the long-term. Many quantum communications technologies rely upon the distribution of entanglement; thus, this network could pave the way to making this a reality.

Siddarth Joshi et al, 2020, ‘A trusted node–free eight-user metropolitan quantum communication network’, Science Advances, Vol. 6, no. 36. DOI: 10.1126/sciadv.aba0959

Image credit: Soeren Wengerowsky