Perfect secrecy has come a step
closer with the launch of the world’s first computer network protected
by unbreakable quantum encryption at a scientific conference in Vienna.
The network connects six locations
across Vienna and in the nearby town of St Poelten, using 200 km of
standard commercial fibre optic cables.
Quantum Cryptography is inherently unbreakable !
Quantum cryptography is completely different from the kinds of security schemes used on computer networks today.
These are typically based on complex
mathematical procedures which are extremely hard for outsiders to crack
but not impossible given sufficient computing resources or time.
But quantum systems use the laws of quantum theory, which have been shown to be inherently unbreakable.
“All quantum security schemes are based
on the Heisenberg Uncertainty Principle, on the fact that you cannot
measure quantum information without disturbing it,” he explained.
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
- Anton Zeilinger, Vienna University
“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 practice this means using the
ultimate quantum objects: photons, the “atoms of light”. Incredibly
faint beams of light equating to single photons fired a million times a
second raced between the nodes in the Vienna network.
Each node, housed in a different Siemens
office (Siemens has provided the fibre links), contains a small rack of
electronics – boxes about the size of a PC – and a handful of sensitive
light detectors.
Numerical key
From the detected photons, a totally
secret numerical key can be distilled, which encodes the users’ data
much like the keys used in normal computer networks do.
The advantage is that no-one else can know the key without revealing themselves.
As we saw in the demonstration, when an
intruder did try to listen in on the quantum exchange, photons became
scrambled, and a rise in the error rate at the node detectors signalled
the attack. The system automatically shut down without being
compromised.
More importantly, the demonstration also showed that the network is robust.
If one quantum link breaks down, the
connections can be re-routed via other nodes, much as phone calls get
re-routed automatically through a telecoms network, so that any two
users on the network can remain in continuous secure contact.
Dr Hannes Huebel of
Vienna University, operating one of the nodes, explained how robustness
was now as important as security in the development of quantum
encryption systems.
“We are constantly in touch with
insurance companies and banks, and they say it’s nearly better that they
lose 10m euros than if the system is down for two hours, because that
might be more damaging for the bank,” said Dr Huebel.
“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.”
Polarised light
The final element of the EU-sponsored
project (called SECO-QC) was the interconnection of different
realisations of quantum cryptography.
There are many ways photons of light can
encode a numerical key: through the direction they’re polarised (like
Polaroid glasses) for example, or the precise timing of their arrival.
Different schemes have different
strengths and weaknesses, and a viable network would have to handle
whatever individual users choose to use, explained the project’s
director, Christian Monyk – just as a mobile phone network has to handle
handsets from many manufacturers.
Quantum cryptography is a surprising outgrowth of recondite arguments that bounced around for decades about the meaning of quantum mechanics.
Albert Einstein, who
discovered the quantum properties of photons of light – indeed,
discovered the very concept of the photon – always resisted quantum
theory’s spooky behaviour, “God does not play dice”, being among his
oft-quoted objections.
But experiments eventually proved that
he apparently does, and also laid the technical foundations for today’s
quantum information revolution – cryptography, teleportation, and
computation.
One of the grandees of quantum science,
Vienna University’s Anton Zeilinger, used the occasion to argue for
continued funding of fundamental science in these increasingly
application-focused days.
“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 said.
“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.”
source : google.
