As with all pure and applied scientific endeavours, there will be periods of steady progress —sometimes grindingly slow, like Edison's drawn-out experimentation to develop a filament for electric light bulbs. There will be failures, and frustrating dead ends. Then will come a spectacular breakthrough.

The field of quantum cryptography is a special case of quantum computing, which relates to general-purpose computation "that makes direct use of distinctively quantum mechanical phenomena, such as superposition and entanglement, to perform operations on data. In a classical (or conventional) computer, information is stored as bits; in a quantum computer, it is stored as qubits (quantum binary digits)."

"The basic principle of quantum computation is that the quantum properties can be used to represent and structure data, and that quantum mechanisms can be devised and built to perform operations with these data."

Currently it's all rather obscure stuff, and rather difficult for the non-specialist to understand. Sooner or later it's likely to bear fantastic fruit, it's only the timing that's uncertain.

In Vienna last week, the SECOQC - Development of a Global Network for Secure Communication based on Quantum Cryptography project held a QKD network demonstration and conference.

The SECOQC say that it was the first QKD demonstration, but I see from ScienceDaily something that I can't reconcile about their claim: "A joint collaboration between Northwestern University and BBN Technologies of Cambridge, Mass., has led to the first demonstration of a truly quantum cryptographic data network. By integrating quantum noise protected data encryption (quantum data encryption or QDE for short) with Quantum Key Distribution (QKD), the researchers have developed a complete data communication system with extraordinary resilience to eavesdropping."

Then Lijun Ma et al. in Experimental Demonstration of an Active Quantum Key Distribution Network with Over Gbps Clock Synchronization say: "We have demonstrated, for the first time to our knowledge, a complete active three-node QKD secured network, which operates at 1.25 Gbps clock rate and is controlled by optical switches. Using this network, a QKD secured video surveillance system has been successfully demonstrated."

The SECOQC's claim of being first seems to be that they've set up a significant network (six nodes, connected by eight fibre-optic links between Vienna and St Pöelten of over 200 Km combined length), and not just a small-scale experimental one.

Anyhow, it's worth reading the SECOQC white paper on quantum key distribution and cryptography that's designed to allow  comparison of QKD with what is currently offered by classical cryptographic techniques.

"Quantum cryptography and especially Quantum Key Distribution (QKD) has triggered intense and prolific research works during the past twenty years and now progresses to maturity" they say.

"QKD enables secret Key establishment between two users, using a combination of a classical channel and a quantum channel, such as an optical fibre link or a free-space optical link. The essential interest of QKD, that is intrinsically linked to the “quantumness” of the signals exchanged on the quantum channel, is that any eavesdropping, on the line can be detected.

"This property leads to a cryptographic properties (sic) that cannot be obtained by classical techniques; this property allows to perform Key Establishment with an extremely high security standard which is known as unconditional or information-theoretic security. Highly security applications are thus the natural candidates for QKD-based security solutions."

PLEASE READ ON...