this post was submitted on 10 Feb 2026
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73
Why Haven’t Quantum Computers Factored 21 Yet? (hackaday.com)
submitted 2 days ago by technocrit@lemmy.dbzer0.com to c/technology@lemmy.world
25 comments fedilink hide all child comments
 

If you are to believe the glossy marketing campaigns about ‘quantum computing’, then we are on the cusp of a computing revolution, yet back in the real world things look a lot less dire. At least if you’re worried about quantum computers (QCs) breaking every single conventional encryption algorithm in use today, because at this point they cannot even factor 21 yet without cheating.

In the article by [Craig Gidney] the basic problem is explained, which comes down to simple exponentials. Specifically the number of quantum gates required to perform factoring increases exponentially, allowing QCs to factor 15 in 2001 with a total of 21 two-qubit entangling gates. Extrapolating from the used circuit, factoring 21 would require 2,405 gates, or 115 times more.

underlying article: https://algassert.com/post/2500

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[–] Treczoks@lemmy.world 2 points 2 days ago (1 children)

For years, quantum computers are only good for doing quantum computing benchmarks. They promise to solve everything, but I'd bet that we get both power from fusion (cold or hot) and have a concious AI decades before a quantum computer solves significant real-world problems.

[–] SmoothOperator@lemmy.world 4 points 1 day ago (1 children)

No serious quantum computer scientist or industry person would claim QC "solves everything". Who is "they"?

[–] Treczoks@lemmy.world 1 points 1 day ago (1 children)

This "everything" was meant as an exaggeration. But it comes close for nearly every article (or press release disguised as an article) in the press.

[–] SmoothOperator@lemmy.world 2 points 22 hours ago (1 children)

QC has well-founded expected applications within chemistry, factorisation and optimization. Anything else is hyperbole at this point.

[–] Treczoks@lemmy.world 0 points 19 hours ago (1 children)

Tell this to the people who try to sell it as the one big computational solution.

[–] SmoothOperator@lemmy.world 1 points 17 hours ago

I am! Tell me who it is, and I'll kick their butts.