Quantum Communications

Toshiba Europe, GÉANT, PSNC and Anglia Ruskin University announce the first demonstration of Quantum Key Distribution within commercial telecommunication networks.

Quantum communications harness quantum phenomena like superposition and entanglement to enhance information transfer between remote nodes.  The key benefits of these techniques are the ability to be able to detect if communications have been intercepted or modified en-route. Which makes these techniques ideal for highly sensitive data interchange.

However, coherent quantum communications, essential for typically phase-based quantum internet architectures, require optical coherence among nodes and typically involve single-photon interference. Within laboratory environments the challenges of preserving optical coherence and integrating advanced

single-photon detectors  can be managed through careful implementation and isolation techniques (even vibrations of the fibre optics can affect coherence). However commercial telecommunications implementations cannot easily provide this highly controlled environment and so the deployment in existing telecommunication networks has been extremely difficult to achieve and often limited to metro-scale implementations – particularly in the financial services sector where the costs of dedicated infrastructure can be supported.

It should be noted that even within these dedicated systems, the nature of quantum coherence means that the data transfer rates achievable are still tiny (much less than 1kbit/s). This is of course impractical for any data transfer activity but is highly suitable for the distribution of encryption keys and in particular symmetric encryption keys.

GÉANT, Toshiba Europe limited, PSNC and the Anglia Ruskin University came together to work on the first major in-the-field demonstration of practical quantum communications using telecoms standard equipment and infrastructure.

The experiment was conducted in Germany, with access to the network infrastructure provided by GÉANT. Communication was established over a link spanning 253.9 km between Frankfurt and Kehl with a 56.0 dB loss and a relay in Kirchfeld, approximately three-fifths of the way. This setup forms a star-shaped quantum network with three nodes: two transmitters, at the network’s edge, and a central relay receiver.

The central relay is connected to each transmitter by a fibre duplex cable and all equipment was housed within standard telecom racks in colocation data centres, functioning alongside existing telecommunications gear. The network’s geographical and functional layout, including the fibre links and system elements, is shown here.

Employing the Twin Field Quantum Key Distribution protocol, a key distribution rate of 110 bit/s over 254 km was achieved.

Importantly, this system features measurement-device-independent properties and non-cryogenically cooled detectors, and represents the first effective quantum repeater implementation on telecom infrastructure, the longest practical quantum key distribution deployment to date, and validates the feasibility of a phase-based quantum internet architecture.

Symmetry vs Asymmetry

Most communication systems (and in particular the TLS methods used for internet security) use a mixture of Asymmetric and Symmetric encryption.

Asymmetric encryption uses a public encryption key and a private decryption key. This allows for users of public services to access data securely. However because of the processing overhead of asymmetric encryption and decryption (particularly as key lengths increase) usually the asymmetric encryption is used solely to exchange a simpler symmetric key.

Symmetric keys can be equally secure for the process of encryption and decryption indeed in some circumstances they can be more secure. They are also faster and less processor intensive in use. But the difficulty arises in the exchange of the key. If this key exchange is intercepted then the eavesdropper can view all the data encrypted using that key trivially easily.

The use of quantum key exchange enables the sharing of symmetric keys with confidence that the keys are secure and have not been intercepted.

This study marks the first successful integration of coherent quantum communications within a commercial telecom infrastructure outside of dedicated metro systems. For more information visit.
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