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