From: jamesd@netcom.com (James A. Donald)
Date: Mon, 3 Oct 94 14:14:08 PDT
To: scmayo@rschp2.anu.edu.au (Sherry Mayo)
Subject: Re: Manufacturing quantum computers
In-Reply-To: <9410030416.AA10229@toad.com>
Message-ID: <199410032113.OAA29471@netcom8.netcom.com>
MIME-Version: 1.0
Content-Type: text/plain


Sherry Mayo writes
> Regarding the quantum cryptography thread: Some people expressed the
> view that although the idea may be workable, the manufacturing technology
> was a long way of being able to produce quantum computers.
> The quantum dot design proposed by Eckert et al for a quantum "factorisation
> engine" requires 100000 quantum dots (to factorise RSA-129 or similar)
> which are each about 10nm across to be fairly densly packed onto a 
> chip. I'm not so sure about this being 'a long way off' in terms of materials
> technology,


Current art is fairly close to making components whose interaction
requires a full quantum description.

To make a quantum computer from such components requires that
that the components be orders of magnitude faster and more
reversible.

Presently known quantum algorithms cannot tolerate the loss of 
a single quantum of energy, as this will introduce
vacuum noise into the data.

The longer the algorithm takes, the less energy there
is in a single quantum of energy, thus the components
for any long quantum algorithm, such as factoring a 1024 bit
number, must be very fast indeed (near infrared frequencies)
and extraordinarily efficient (fully reversible classical,
non quantum computation.)

Although quantum computers are interesting and important,
they have no immediate practical relevance to cryptography.

Error tolerant algorithms could change the picture substantially,
but they would still require components far beyond current
art.




-- 
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We have the right to defend ourselves and our
property, because of the kind of animals that we              James A. Donald
are.  True law derives from this right, not from
the arbitrary power of the omnipotent state.                jamesd@netcom.com