Scientists Unveil Unbreakable Quantum Encryption Network

The world’s first “unbreakable” quantum encryption network was unveiled this week at a science conference in Vienna.

The EU-sponsored network (called SECOQC) uses 200 km of fiber optic cables, provided by Siemens, to interconnect six locations in Vienna and the neighboring town of St. Poelten. 

Quantum cryptography is markedly different from current security schemes, which are based on complex mathematical procedures that are extremely difficult, but not impossible, for outsiders to crack.

Instead, quantum systems harness the inherently unbreakable laws of quantum theory.  The notion of quantum cryptography was established 25 years ago by Charles Bennett of IBM and Gilles Brassard of Montreal University, who was in attendance this week in Vienna to observe the new network in action.

"All quantum security schemes are based on the Heisenberg Uncertainty Principle, on the fact that you cannot measure quantum information without disturbing it," Brassard told BBC News.

"Because of that, one can have a communications channel between two users on which it’s impossible to eavesdrop without creating a disturbance. An eavesdropper would create a mark on it. That was the key idea."

In reality this means using photons, atoms of light that are the ultimate quantum objects. In the Vienna network, amazingly faint beams of light equating to single photons fired a million times each second surged between the network nodes.

A uniquely secret numerical key can be distilled from the detected photons, which encodes the users’ data much the same way as keys used in traditional computer networks do today. 

The advantage of quantum systems is that no-one else can discover the key without revealing themselves.  This was proven in a demonstration in which an intruder tried to listen in on the quantum exchange. Photons became subsequently scrambled, and a rise in the error rate at the node detectors revealed the attack.  The system then automatically shut down without being compromised.

The demonstration also proved the robust nature of the quantum encryption network, in that if one quantum link breaks down, the connections re re-routed via other nodes, similar to the way phone calls are automatically re-routed through a telecom network so that users remain in continuous and secure contact.

"We are constantly in touch with insurance companies and banks, and they say it’s nearly better that they lose 10 million euros than if the system is down for two hours, because that might be more damaging for the bank," said Dr. Hannes Huebel of Vienna University, who operated one of the nodes.

"So that’s what we have to prove, that we have a reliable system that delivers quantum keys for several weeks without interruption, and then they might be more interested."

The final part of the SECO-QC project was the interconnection of different versions of quantum cryptography.

There are many ways that photons can encode a numerical key, including the direction they’re polarized or the precise timing of their arrival.

Since each scheme has different strengths and weaknesses, a viable network would have to be capable of managing whatever scheme an individual user might choose to use, said Christian Monyk, the project’s director. Monyk likened this to the way mobile phone networks must handle handsets from many different handset manufacturers.

Quantum cryptography is a surprising outgrowth of complex debates taking place over many years about the meaning of quantum mechanics.

Albert Einstein, who discovered the very concept of the photon along with its quantum properties, dismissed the theory’s spooky behavior.

The words "God does not play dice" was among his many cited objections.

However, science ultimately proved he apparently does, something that has paved the way for the current quantum information revolution in computation, cryptography and teleportation.

Vienna University’s Anton Zeilinger, one of the leaders of quantum science, used this week’s demonstration to call for continued funding of fundamental science in these increasingly application-focused times.

"Real breakthroughs are not found because you want to develop some new technology, but because you are curious and want to find out how the world is," Dr Zeilinger told BBC News.

"It may not have surprised the founding fathers of quantum science that technology has advanced so that you can play with individual quantum systems, in great detail.

"Maybe this would not surprise, but what could surprise them is that people are thinking and doing practical applications."

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Image Caption: A Computer simulation done by "Die Drahtwarenhandlung" of the Quantumcryptography-Network.

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On the Net:

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