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From:	The Powerhouse <P.C.Steele@*********.AC.UK>
Subject:	Quantum cryptograph - a precis
Date:	Mon, 8 Aug 1994 16:54:36 +0100

Message no. 1 There seems to be alot of confusion on this subject which is understandable
as most people have never done quantum physics.

To summarise, the original article stated that by sending one particular photon
whose measurements had been measured in one dimension, that the photon could
be used as a key in an encryption system. The recievers would measure the
a different dimension of photon, do lots of high powered maths and see if the
two things tally <Jane correct me on this if I'm wrong :) >

The idea behind the fact that if someone is observing the photon then they
force a change upon the photon is fairly well known. Based I believe from
Hiesenberg's <sp?> uncertainty principle which has various forms but one is
that the position of a photon and it's energy can never both be known at the
same time <again correct me if I'm wrong here, it's been a few years since I
studied this subject>.

So that's the idea behind it all <all be it with a few technical
inacuracies :) >. However the problem comes around in creating devices that
can measure exactly all the relevant stuff on a photon, producing that single
electron <not so difficult :) >, creating a medium whereby that photon can
be transmitted without changing it's properties <that's the real problem>,
and finally creating a device that can measure precisely one photon on receiving
it.

Simply put, there's no dammed way it's going to be practical in the next 10
years. In the future however, who knows ? Maybe waveguides which are made of
superconductors and can force the photons to stay on the right track through a
vacumn by means of a magnetic field will be possible. If there ever is a
solution expect it to be along those sort of lines.

Phill.
--
Phillip Steele - Email address P.C.Steele@***.ac.uk | Fighting against
Department Of Electrical & Electronic Engineering | Political Correctness !
University Of Newcastle Upon Tyne, England |
Land of the mad Geordies | The Powerhouse

From:	Janne Jalkanen <jalkanen@*********.CERN.CH>
Subject:	Re: Quantum cryptograph - a precis
Date:	Tue, 9 Aug 1994 10:24:00 +0200

Message no. 2 On Mon, 8 Aug 1994, The Powerhouse wrote:

> To summarise, the original article stated that by sending one particular
photon
> whose measurements had been measured in one dimension, that the photon could
> be used as a key in an encryption system. The recievers would measure the
> a different dimension of photon, do lots of high powered maths and see if the
> two things tally <Jane correct me on this if I'm wrong :) >

It's Janne, actually. There's a big difference, 'cos Janne is a man's
name. [Sorry to disappoint everyone ;-)]

Basically you are correct, except that you don't need high-powered maths.
Very simple maths will do. If the transmission is encrypted, then you'll
need a computer, otherwise you can easily do with pen and paper ;)

> Hiesenberg's <sp?> uncertainty principle which has various forms but one is
> that the position of a photon and it's energy can never both be known at the
> same time <again correct me if I'm wrong here, it's been a few years since I
> studied this subject>.

Heisenberg's Uncertainty Principle states that Time*Energy > Planck's
Constant / (2*Pi). [Actually it's a bit more complicated ;)], but what it
basically says that you cannot measure the exact place AND energy of a
particle. Only the either one. That means, you can never know where a
given particle is - you can measure it exactly once and then it will be
in a completely new place and has completely new properties.

> inacuracies :) >. However the problem comes around in creating devices that
> can measure exactly all the relevant stuff on a photon, producing that single
> electron <not so difficult :) >, creating a medium whereby that photon can
> be transmitted without changing it's properties <that's the real problem>,
> and finally creating a device that can measure precisely one photon on
receiving
> it.

Sending and receiving photons is constantly done here in CERN. Not that
difficult, really - the procedures are straightforward and when the
technology advances, they'll be more readily available. As for the
medium, they have a circular vacuum tube, that is 27 kilometers in
diameter. Not very cost-effective, I'm afraid ;)

> Simply put, there's no dammed way it's going to be practical in the next 10
> years. In the future however, who knows ? Maybe waveguides which are made of
> superconductors and can force the photons to stay on the right track through a
> vacumn by means of a magnetic field will be possible. If there ever is a
> solution expect it to be along those sort of lines.

This is exactly what is done here in CERN. The trouble is, photons have no
charge and thus cannot be controlled by magnetic beams. BUT there are
other particles which could be used for the purpose. A muon beam for
example. Consult your friendly Quantum Physics Handbook to see what I'm
talking about ;)

However - for all the enterprising GM's out there - it is very possible
that someone in Shadowrun World has invented a method of making all of
this possible. Now that'd make an interesting scenario idea... A big corp
invents something like this and suddenly, there are tens of operatives
from other companies trying to steal the secret... You could hire the
runners as a penetration team or a protection team. And the corps would
probably want the secret REAL hard.

> Phill.

Janne Jalkanen ///! For those who have to fight for it
jalkanen@******.cern.ch /// ! life has a flavor
Janne.Jalkanen@***.fi \\\/// ! the protected will never understand
-'Keep on going...' \XX/ ! (anonymous, Viet Nam, 1968)

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