X-Message-Number: 21120
From: "michaelprice" <>
References: <>
Subject: quantum computer
Date: Tue, 11 Feb 2003 08:16:39 -0000

Thomas Donaldson is more optimistic than me about the potential of quantum
computers.  I agree with

> So long as we and the external world do not interfere
> in their calculations in any way, they can operate
> simultaneously on ALL the possible states of their parts,
> which may be electrons in one form or another.

The problem starts with:

> It's your final result that you read off
> from them which comes out uniquely.

I have never seen a cogent explanation of how the result is read out of a
quantum computer, in a fashion that is superior to a classical computer.
The example that James Swayze gave of Bucksbaum's "Library of Congress in an
electron" fails at this reading out stage; this major difficulty is only
obscured because his experiments are operating on millions of identically
prepared electrons.  Although I am no expert in the field I have read a
number of proposals for quantum computers; the only one that made sense to
me improved on the search time from O(N) to O(root(N)), for a list with N
items in it.  Interestingly Bucksbaum's work is based on it.  David Deutsch
wrote a paper about extracting information from a completed quantum computer
but it seemed to me that the result bandwidth was no better than with a
classical device, except for the most artificially constructed problems.

> Most of the literature on such computers is in physics journals,
> which you of all people ought to be able to read. If nothing else,
> a quantum computer would be much more compact than a
> parallel computer. Given that quantum principles were recently
> used to actually build a quantum encoder-decoder, I am optimistic
> that such computers can be built, though it will take some time.

Quantum cryptography, which I have no reservations about, is not the same as
quantum computing.

BTW, I am happy to accept the offer of resuming the electron identity debate
in the post-Singularity, brain-augmented future - or indeed anytime someone
actually has something new to add rather than just re-iterate points I've
already addressed.  Otherwise the debate will probably last until the
Singularity
arrives..

Cheers,
Michael C Price
----------------------------------------
http://mcp.longevity-report.com
http://www.hedweb.com/manworld.htm

Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=21120