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From: Lawrence D'Oliveiro <ldo@nz.invalid>
Newsgroups: comp.arch
Subject: Re: Is Intel exceptionally unsuccessful as an architecture designer?
Date: Thu, 19 Sep 2024 20:53:44 -0000 (UTC)
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On Thu, 19 Sep 2024 12:59:42 +0200, Terje Mathisen wrote:

> From my recent reading, it seems like factoring 21 (5 bits) requires at
> least 5+10=15 bits all staying entangled, plus a number of additional
> bits for error correction.

The noise factor was something the original ideas about quantum computers 
had not taken into account.

But it’s pretty obvious why it happens: “quantum” computing was something 
thought up by people who took the “many worlds” interpretation of quantum 
theory just a little too seriously: if you could take advantage of 
“superposition of states” to run your computation simultaneously across 
multiple alternate universes, you could access a whole lot more computing 
power!

The reason why it doesn’t work is because of conservation of energy. 
Accessing those hypothetical “alternate universes” requires spreading the 
same amount of energy more thinly. And that’s where the noise comes from. 
So ultimately there will be no way to get rid of it.

And that’s why I say “quantum” computing (at least for number-theoretic 
operations) is “trying to get something for nothing”. Ultimately that 
won’t work.