Somewhat related is the work done in "Falling with Style: Factoring up to 255 “with” a Quantum Computer" published in the proceedings of SIGBOVIK 2025 [1]. The author, Craig Gidney [2], successfully factored all odd composite numbers up to 255 using Shor's algorithm, even though the quantum circuits involved were such that any meaningful output would be overwhelmed by noise (and indeed, performance was maintained when the circuits were replaced by a random number generator).
> To my knowledge, no one has cheated at factoring in this way before. Given the shenanigans pulled by past factoring experiments, that’s remarkable.
[2] Who has previous experience in cheating at quantum factoring: see "Factoring the largest number ever with a quantum computer", posted April Fools' Day 2020 at https://algassert.com/post/2000
> In the Callas Normal Form, the factors are integers p = 2^{n-1}
and q = 2^{m+1}, where n ≤ m, and p and q are ideally prime, but don’t have to be.
The paper's formatting clearly went wrong here, as it should have read p = 2^n - 1 and q = 2^m + 1.
The "Proposed Quantum Factorisation Evaluation Criteria" are excellent, but for measuring progress, the required minimum factor size of 64 bits is too large. A good milestone would be a quantum circuit that can factor the product of any pair of 5-bit primes {17,19,23,29,31}.
I checked in with Scribble as he did the typesetting. He apologizes for the error but says working without opposable thumbs makes the work more challenging.
I think 8 bit primes is probably a better minimum. 5 bits is still small enough that randomly choosing a 5 bit factor will succeed 40% of the time. This is especially problematic since Shor's algorithm only has a 50% success probability per round, so you need some extra bits to be able to distinguish a correctly working quantum computer from a random number generator.
"Just as a thought experiment, what's the most gutless device that could
perform this "factorisation"? There's an isqrt() implementation that uses
three temporaries so you could possibly do the square root part on a ZX81, but
with 1k of RAM I don't think you can do the verification of the guess unless
you can maybe swap the values out to tape and load new code for the multiply
part. A VIC20 with 4k RAM should be able to do it... is there a programmable
calculator that does arbitrary-precision maths? A quick google just turns up
a lot of apps that do it but not much on physical devices.
You can verify in limited memory by repeatedly verifying modulo a few small integers. If that works, then by Chinese remainder theorem the main result also holds.
Yeah there's a reason that the quantum computing field has moved away from attempting factorisations. Not that there's not still hype and misleading claims being punished, but the hardware has improved a ton since 2001 and ever closer to actual useful quantum computation (such as large size quantum chemistry calculations).
Are those useful computations in the room with us right now? No, but seriously, I feel like factorization is the one application that could justify those massive investments QC is receiving (even though it would probably make the world strictly worse...).
All those other applications, no matter how neat, I feel are quite niche. Like, "simulate pairs of electrons in the Ising model". Cool. Is that a multi-billion dollars industry though?
If results from methods with higher electronic structure accuracy than DFT (MP2, couple cluster) can be made cheap enough, it would hugely disrupt industrial chemistry, medical experimentation, pharmaceuticals, the energy sector, etc.
Ground state and activation energy estimation for chemistry would be really useful. I know chemists are looking specifically at nitrogen fixation as one useful example.
Or as another example, I'm currently at a conference listening to a PhD student's research on biomolecular structure prediction (for protein design).
Cool stuff and thanks for the link, I'll have to learn about it when I have a bit more time.
I've always heard Qalgs for chemistry compared to classical methods though. Why do you think chemists are using CCSD and similar methods rather than the FT-ICR mass spectroscopy?
Factorization could have number theory implications I suppose. Using quantum effects to break cryptography wouldn't have any real long term advantages unless you aspired to be some sort of a supervillain.
If you want O($10 billion per year) of funding, those numbers can only come from having $10 billion a year of impact balanced against your chance of success. The only application of QC worth $100+ billion is breaking cryptography.
PQC is as much a tool to reduce funding for QC as it is a tool against an actual eventual quantum computer.
>...6502 microprocessor from 1975. Since this processor uses transistors, and transistors work by using quantum effects, a 6502 is as much a quantum device as is a D-Wave “quantum computer”.
I'm not sure that is true in the way it is intended. The NMOS transistors used in the 6502 were quite large and worked on the basis of electrostatic charges ... as opposed to bipolar transistors that are inherently quantum in operation.
Of course it is now understood that everything that does anything is at some level dependent on quantum effects. That would include the dog...
> The NMOS transistors used in the 6502 were quite large and worked on the basis of electrostatic charges ... as opposed to bipolar transistors that are inherently quantum in operation
Forming a conductive channel in silicon in any FET and semiconductivity in general is an inherently quantum effect too, right?
Traditionally I don't think it was considered to be specially a quantum effect. That, again was because bipolar transistors specifically work over a quantum band gap ... and bipolar transistors proceeded mosfets.
So only a quantum effect to the extent all effects are at some level quantum.
The intention is to say that the D-Wave isn't a quantum computer at all. The comparison isn't quite literally true, but it's definitely the case that what D-Wave does is very different from the general purpose qubits that we mean when we say "quantum computer".
>Similarly, we refer to an abacus as “an abacus” rather than a
digital computer, despite the fact that it relies on digital manipulation to effect its computations.
Somewhat related is the work done in "Falling with Style: Factoring up to 255 “with” a Quantum Computer" published in the proceedings of SIGBOVIK 2025 [1]. The author, Craig Gidney [2], successfully factored all odd composite numbers up to 255 using Shor's algorithm, even though the quantum circuits involved were such that any meaningful output would be overwhelmed by noise (and indeed, performance was maintained when the circuits were replaced by a random number generator).
> To my knowledge, no one has cheated at factoring in this way before. Given the shenanigans pulled by past factoring experiments, that’s remarkable.
[1] https://sigbovik.org/2025/; standalone paper is also available in the code repository https://github.com/strilanc/falling-with-style
[2] Who has previous experience in cheating at quantum factoring: see "Factoring the largest number ever with a quantum computer", posted April Fools' Day 2020 at https://algassert.com/post/2000
God, I've heard Gidney's name so many times in the QC conference I'm attending, and in my research the last few months.
I really hope he eventually gets the recognition he deserves, outside of just experts in the field.
> In the Callas Normal Form, the factors are integers p = 2^{n-1} and q = 2^{m+1}, where n ≤ m, and p and q are ideally prime, but don’t have to be.
The paper's formatting clearly went wrong here, as it should have read p = 2^n - 1 and q = 2^m + 1.
The "Proposed Quantum Factorisation Evaluation Criteria" are excellent, but for measuring progress, the required minimum factor size of 64 bits is too large. A good milestone would be a quantum circuit that can factor the product of any pair of 5-bit primes {17,19,23,29,31}.
I checked in with Scribble as he did the typesetting. He apologizes for the error but says working without opposable thumbs makes the work more challenging.
I think 8 bit primes is probably a better minimum. 5 bits is still small enough that randomly choosing a 5 bit factor will succeed 40% of the time. This is especially problematic since Shor's algorithm only has a 50% success probability per round, so you need some extra bits to be able to distinguish a correctly working quantum computer from a random number generator.
Thanks. The flawed superscripting was bugging me too. Easily detectable but a reviewer should have caught it before publication.
I remember Peter Gutmann posting about this on the metzdowd cryptography mailing list in March. Fun to see this a few months later.
It starts here: https://www.metzdowd.com/pipermail/cryptography/2025-Februar...
This part is from farther down thread:
"Just as a thought experiment, what's the most gutless device that could perform this "factorisation"? There's an isqrt() implementation that uses three temporaries so you could possibly do the square root part on a ZX81, but with 1k of RAM I don't think you can do the verification of the guess unless you can maybe swap the values out to tape and load new code for the multiply part. A VIC20 with 4k RAM should be able to do it... is there a programmable calculator that does arbitrary-precision maths? A quick google just turns up a lot of apps that do it but not much on physical devices.
Peter."
You can verify in limited memory by repeatedly verifying modulo a few small integers. If that works, then by Chinese remainder theorem the main result also holds.
This paper is both a hilarious parody and a genuinely valuable contribution to the literature.
(Beware of typo pointed out by tromp here.)
Yeah there's a reason that the quantum computing field has moved away from attempting factorisations. Not that there's not still hype and misleading claims being punished, but the hardware has improved a ton since 2001 and ever closer to actual useful quantum computation (such as large size quantum chemistry calculations).
Are those useful computations in the room with us right now? No, but seriously, I feel like factorization is the one application that could justify those massive investments QC is receiving (even though it would probably make the world strictly worse...).
All those other applications, no matter how neat, I feel are quite niche. Like, "simulate pairs of electrons in the Ising model". Cool. Is that a multi-billion dollars industry though?
If results from methods with higher electronic structure accuracy than DFT (MP2, couple cluster) can be made cheap enough, it would hugely disrupt industrial chemistry, medical experimentation, pharmaceuticals, the energy sector, etc.
Ground state and activation energy estimation for chemistry would be really useful. I know chemists are looking specifically at nitrogen fixation as one useful example.
Or as another example, I'm currently at a conference listening to a PhD student's research on biomolecular structure prediction (for protein design).
One of the few genuinely useful accomplishments of modern "AI" has been protein structure prediction. I wonder if we still even need QC for this.
Energy levels and activation energies can be acquired much more simply from Fourier Transform - Ion Cyclotron Resonance - Mass Spectroscopy...
Its a device that makes and analyzes at the same time, check out this primer:
https://warwick.ac.uk/fac/sci/chemistry/research/oconnor/oco...
Cool stuff and thanks for the link, I'll have to learn about it when I have a bit more time.
I've always heard Qalgs for chemistry compared to classical methods though. Why do you think chemists are using CCSD and similar methods rather than the FT-ICR mass spectroscopy?
Factorization could have number theory implications I suppose. Using quantum effects to break cryptography wouldn't have any real long term advantages unless you aspired to be some sort of a supervillain.
If you want O($10 billion per year) of funding, those numbers can only come from having $10 billion a year of impact balanced against your chance of success. The only application of QC worth $100+ billion is breaking cryptography.
PQC is as much a tool to reduce funding for QC as it is a tool against an actual eventual quantum computer.
> Using quantum effects to break cryptography wouldn't have any real long term advantages unless you aspired to be some sort of a supervillain.
It's of interest to governments, for national security reasons. Quantum computing is an arms race.
>...6502 microprocessor from 1975. Since this processor uses transistors, and transistors work by using quantum effects, a 6502 is as much a quantum device as is a D-Wave “quantum computer”.
I'm not sure that is true in the way it is intended. The NMOS transistors used in the 6502 were quite large and worked on the basis of electrostatic charges ... as opposed to bipolar transistors that are inherently quantum in operation.
Of course it is now understood that everything that does anything is at some level dependent on quantum effects. That would include the dog...
> The NMOS transistors used in the 6502 were quite large and worked on the basis of electrostatic charges ... as opposed to bipolar transistors that are inherently quantum in operation
Forming a conductive channel in silicon in any FET and semiconductivity in general is an inherently quantum effect too, right?
Traditionally I don't think it was considered to be specially a quantum effect. That, again was because bipolar transistors specifically work over a quantum band gap ... and bipolar transistors proceeded mosfets.
So only a quantum effect to the extent all effects are at some level quantum.
The intention is to say that the D-Wave isn't a quantum computer at all. The comparison isn't quite literally true, but it's definitely the case that what D-Wave does is very different from the general purpose qubits that we mean when we say "quantum computer".
this was great. I had no idea quantum factorisation was cooking their books!
The dog is funny but it just means, pick actually "random" numbers from a bigger range than the staged phony numbers quantum factorisation uses.
>We use the UK form “factorise” here in place of the US variants “factorize” or “factor” in order to avoid the 40% tariff on the US term
Brilliant.
Yeah, they are really on point...
>Similarly, we refer to an abacus as “an abacus” rather than a digital computer, despite the fact that it relies on digital manipulation to effect its computations.
This is probably one of the first academic papers I've ever read completely from beginning to end in one go.