X-Message-Number: 21089
From: "michaelprice" <>
References: <>
Subject: Quantum Computers 
Date: Sat, 8 Feb 2003 00:06:41 -0000

James Swayze :
> I already pointed to a now available technology that apparently, unless
> I am simply fundamentally wrong, already shows us that electrons differ.
> Please read the article at the following URL and make your own
> conclusions.
[ http://www.eetimes.com/story/OEG20000831S0019 ]

> Or simply trust mine which are that if this technology is not a hoax,
> chiefly that a laser can encode enough information to house even the
> entire library of Congress on the wave function of a single electron,
> then obviously an electron can be changed from its original form.

Thanks, James, for the pointer, which prompted me to do a bit of additional
hunting around that has been most illuminating.

The experimenters seem to have overlooked an important fact which renders
their entire quantum computing project (and perhaps all quantum computing
attempts) pointless.   (Or more likely, they are deliberately being vague,
so as to secure future funding...)  In brief, no, the technology is not a
hoax and the article is correct; a single electron's wavefunction (=
probability amplitude) can encode an unlimited amount of information.

The good news stops there, though, since there is no way of extracting this
information from a single electron.  A measurement on (or any irreversible
interaction with) the electron causes the infamous collapse of the
wavefunction, with the associated loss of information.  In the experiment
mentioned they are storing and retrieving the information from a million
identical caesium atoms simultaneously. (see
that makes this clear.)  By operating on such a
large number of electrons or atoms they are able to exploit the
million-fold parallelism present and thereby extract information to
digitally reconstruct the electrons' wavefunctions.  In this experiment, the
information recoverable is limited 3 bits per electron.  The more atoms used
the more information they can recover.

In effect they haven't got a new-fangled quantum computer (as they claim or
think) but an old-fashioned parallel-processing computer.

Michael C Price

Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=21089