Why Haven’t Quantum Computers Factored 21 Yet?

Submitted ⁨⁨2⁩ ⁨days⁩ ago⁩ by ⁨technocrit@lemmy.dbzer0.com⁩ to ⁨technology@lemmy.world⁩

https://hackaday.com/2026/02/09/why-havent-quantum-computers-factored-21-yet/

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: algassert.com/post/2500

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Comments

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KoboldCoterie@pawb.social ⁨2⁩ ⁨days⁩ ago
I rarely feel as stupid as when reading anything about quantum computing. The whole field could just be a giant in-joke where none of it exists and they’re all just spouting nonsense technical jargon to confound the plebs, and I’d be oblivious.

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- BreadstickNinja@lemmy.world ⁨1⁩ ⁨day⁩ ago
  There’s a good 3blue1brown video that walks through the actual math they can perform, which does a lot to temper expectations about what they can accomplish and how much of an improvement they would be over digital computers for certain types of problems.
  
  Here’s the YouTube link, or search for “But What Is Quantum Computing? (Grover’s Algorithm)” on your preferred front-end: youtu.be/RQWpF2Gb-gU
  
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- cecilkorik@piefed.ca ⁨2⁩ ⁨days⁩ ago
  Is it real, or is it a giant financial marketing bubble waiting for its moment to consume the world economy? Let’s watch what happens with the AI bubble to find out.
  
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  - astropenguin5@lemmy.world ⁨2⁩ ⁨days⁩ ago
    I don’t think quantum computing is a bubble at all, at least not yet. It’s still firmly in the stage of being explored and understood in a healthy way. I could see it having the possibility of being a bubble, but it would take significant advances in making it more available.
    
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  - Gust@piefed.social ⁨2⁩ ⁨days⁩ ago
    Quantum computing is trying to be ai, in the sense that it does have niche scientific uses it excels at but tech bro types want it to be the next general computer so they can make their empire on it. The only use case I’ve seen it excel at so far is generating precisely tailored probability distributions, which end up mostly being useful for simulating different models for quantum field theory. Even then I’ve only seen that in looped fiber implementations, which imo are a stretch on the definition of quantum computer.
    
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- I_Has_A_Hat@lemmy.world ⁨2⁩ ⁨days⁩ ago
  Every time I see a picture of a quantum computer, it just looks like a bunch of Galileo thermometers bundled together. So maybe you’re on to something lol
  
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- Naich@lemmings.world ⁨2⁩ ⁨days⁩ ago
  Come off it. Next you’ll be saying that lemmyverse.link/lemmy.ca/c/vxjunkies are just making it up.
  
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  - bamboo@lemmy.blahaj.zone ⁨2⁩ ⁨days⁩ ago
    This syntax should work in most Lemmy clients natively: !vxjunkies@lemmy.ca
    
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  - AbidanYre@lemmy.world ⁨2⁩ ⁨days⁩ ago
    That’s giving a 404. Kobold might be on to something.
    
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- Imgonnatrythis@sh.itjust.works ⁨2⁩ ⁨days⁩ ago
  I think you are thinking of recycling.
  
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bamboo@lemmy.blahaj.zone ⁨2⁩ ⁨days⁩ ago
The linked paper, “Replication of Quantum Factorisation Records with an 8-bit Home Computer, an Abacus, and a Dog” is also a great breakdown of how much the quantum factoring is more of a parlor trick and not practical for factoring RSA Keys, mainly since the prime factors are only a few bits off of each other and from the square root of the number being factored.

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- A_A@lemmy.world ⁨2⁩ ⁨days⁩ ago
  a well trained dog outperforms current quantum-made calculations 👍🥳
  
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- lucullus@discuss.tchncs.de ⁨1⁩ ⁨day⁩ ago
  
  We hypothesise that the production of fully entangled sheep is easy, given how hard it can be to disentangle their coats in the first place. The logistics of assembling the tens of thousands of sheep necessary to factorise RSA-2048 numbers is left as an open problem
  
  Omg, I simply cannot! Thanks for brightening my day with this paper XD
  
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- MetalSlugX@piefed.social ⁨2⁩ ⁨days⁩ ago
  Seriously recommend this. I saw it a while back and found it highly informative
  
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Laser@feddit.org ⁨2⁩ ⁨days⁩ ago
It’s Ford’s Quantum Computer, it will factor any number you want, as long as it’s 15.

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Treczoks@lemmy.world ⁨2⁩ ⁨days⁩ ago
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.

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- SmoothOperator@lemmy.world ⁨1⁩ ⁨day⁩ ago
  No serious quantum computer scientist or industry person would claim QC “solves everything”. Who is “they”?
  
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  - Treczoks@lemmy.world ⁨1⁩ ⁨day⁩ ago
    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.
    
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PointyFluff@lemmy.ml ⁨2⁩ ⁨days⁩ ago
Quantum Computers are bullshit.

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