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From: David Brown <david.brown@hesbynett.no>
Newsgroups: comp.arch
Subject: Re: Is Intel exceptionally unsuccessful as an architecture designer?
Date: Thu, 19 Sep 2024 11:35:41 +0200
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On 19/09/2024 09:44, Niklas Holsti wrote:
> On 2024-09-19 2:47, Lawrence D'Oliveiro wrote:
>> On Wed, 18 Sep 2024 20:09:53 GMT, Anton Ertl wrote:
>>
>>> He mentioned that several physics breakthroughs
>>> are needed for quantum computing to become useful.
>>
>> The biggest one would be getting around the fundamental problem that you
>> can’t get something for nothing.
> 
> 
> Stupid argument. Look at the effort and tech it takes to make quantum 
> computers... that is not "nothing".
> 
> 
>> The promise of an exponential increase in computing power for a linear
>> increase in the number of processing elements sounds very much like
>> “something for nothing” under another name, wouldn’t you say?
> 
> 
> No, it is exploiting the very non-intuitive nature of quantum 
> entanglement to create an exponential number of collective states of a 
> linear number of elements. Medieval arguments about "nothing" vs 
> "something" don't work there.
> 

Quantum computing certainly gives you some tricks that are hard to 
replicate with classical computers.  (And of course some quantum effects 
are impossible to replicate classically, but those are not actually 
computations.)

But it is still ultimately limited in many ways.  Landauer's principle 
about the minimal energy costs of calculations applies equally to 
quantum calculations.

The practical limitations for quantum computers are far more 
significant.  Roughly speaking, when you entangle more states at once, 
you need tighter tolerances to maintain coherence, which translates to 
lower temperatures, higher energy costs, and lower times to do your 
calculations.  And to be useful, you need large numbers of qubits, which 
again makes maintaining coherence increasingly difficult.

I'm sure that there will be breakthroughs that improve some of this, but 
I am not holding my breath - I don't believe quantum computers will ever 
be cost-effective for anything but a few very niche problems.  Currently 
they have only beat classical computers in tasks that involve simulating 
some quantum effects.  That's a bit like noticing that soap bubble 
computers are really good at solving 2D minimal energy surface problems.

Remember, the current record for Shor's algorithm is factorising 21 into 
3 x 7.  Factorising 35 is still beyond current engineering levels.