US scientists today claimed to have developed the world's first truly quantum cryptographic data network.

By integrating quantum noise-protected data encryption (QDE) with quantum key distribution (QKD), researchers from the Northwestern University and BBN Technologies of Cambridge, Massachusetts, have developed a complete data communication system which boasts "extraordinary resilience to eavesdropping".

Prem Kumar, professor of electrical engineering and computer science at Northwestern's Robert R. McCormick School of Engineering and Applied Science was co-principal investigator on the project which demonstrated a new way of encrypting data that relies on traditional algorithms and physical principles.

The QDE method, called AlphaEta, makes use of the inherent and irreducible quantum noise in laser light to enhance the security of the system and make eavesdropping much more difficult.

Unlike most other physical encryption methods, AlphaEta maintains performance on a par with traditional optical communications links and is compatible with standard fibre optic networks.

The Northwestern researchers carried out several demonstrations of the compatibility and reach of the AlphaEta system in conventional wave-division multiplexed optical networks.

However, in all these tests the communicating parties, called 'Alice' and 'Bob', had pre-shared encryption keys for use in the AlphaEta system.

The scientists explained that QKD exploits the unique properties of quantum mechanics to securely distribute electronic keys between two parties.

Unlike traditional key distribution, the security of QKD can in theory provide quantitatively secure keys regardless of advances in technology.

Typically, these ultra-secure keys would be used in traditional encryption algorithms to allow for high-speed encrypted communications.

In the present advance, the QKD and the QDE technologies have been interfaced together, forming a truly quantum cryptographic data network.

The combined QKD/AlphaEta system has been demonstrated in a 9km link between BBN headquarters and Harvard University.

The AlphaEta encrypted signal carried OC-3 (155Mbps) Sonet data between the two nodes. A fresh encryption key of about 1Kb was repetitively loaded every three seconds.

In a separate test, the AlphaEta encrypted signal was looped back multiple times to create an effective 36km link where more than 300 consecutive key exchanges were demonstrated.