Cryptography Reference
In-Depth Information
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Yet another problem is that turbulences deflect the light ray. This is why
the current deviation from the ideal is determined concurrently to ensure
that the sender is always directed exactly to the receiver.
Such tricks helped Hughes and his team to demonstrate airborne quantum
cryptography over a distance of 500 meters. 'Big deal', you will probably
say, 'people covered 48 kilometers over fiberglass'. Well, let's not jump to
conclusions yet! Once we have overcome a 2-km airway, we will reach 300 km
into orbit somehow sooner or later! This is so for the simple reason that the
density of air and turbulences decrease quickly as the height increases.
For the time being, however, we will stay on earth, where considerable progress
has been made:
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The 67-km distance between Geneva and Lausanne has been overcome
by fiberglass.
•
Toshiba achieved a transmission rate of 15 bits/s over a 100-km fiberglass
line in Cambridge.
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The most impressive achievement, however, is probably the bridging by
telescope and laser of a 23.4-km beeline between the Wendelstein and
Zugspitze mountains on the German side of the Alps. You can read all
the details about this fascinating work by Matthaus Halder on our Web
site and the Internet at
scotty.quantum.physik.uni-muenchen.de/
publ/matthaeusdiplom.pdf
.
Nothing is impossible, so it seems.
5.9 Quantum Computers. What's Still In There for
Brute Force?
If you think the last point above seemed like witchcraft, you will probably
banish the following into the realm of utopia. You wouldn't be alone. Except for
a group of theoretical physicists, nobody took the 'quantum computer' seriously
for a long time. We had failed to understand that such computers could turn our
ideas about information technology upside down radically. However, I have to
take a run-up to explain this.
You'll probably remember from school that quantum mechanics does not speak
of deterministic states, such as 'power on' or 'power off' (corresponding to bit 0
