[HN Gopher] More on whether useful quantum computing is "imminent"
___________________________________________________________________
More on whether useful quantum computing is "imminent"
Author : A_D_E_P_T
Score : 129 points
Date : 2025-12-21 20:53 UTC (1 days ago)
(HTM) web link (scottaaronson.blog)
(TXT) w3m dump (scottaaronson.blog)
| prof-dr-ir wrote:
| I am confused, since even factoring 21 is apparently so difficult
| that it "isn't yet a good benchmark for tracking the progress of
| quantum computers." [0]
|
| So the "useful quantum computing" that is "imminent" is not the
| kind of quantum computing that involves the factorization of
| nearly prime numbers?
|
| [0] https://algassert.com/post/2500
| bawolff wrote:
| I always find this argument a little silly.
|
| Like if you were building one of the first normal computers,
| how big numbers you can multiply would be a terrible benchmark
| since once you have figured out how to multiply small numbers
| its fairly trivial to multiply big numbers. The challenge is
| making the computer multiply numbers at all.
|
| This isn't a perfect metaphor as scaling is harder in a quantum
| setting, but we are mostly at the stage where we are trying to
| get the things to work at all. Once we reach the stage where we
| can factor small numbers reliably, the amount of time to go
| from smaller numbers to bigger numbers will be probably be
| relatively short.
| jvanderbot wrote:
| From my limited understanding, that's actually the opposite
| of the truth.
|
| In QC systems, the engineering "difficulty" scales very badly
| with the number of gates or steps of the algorithm.
|
| Its not like addition where you can repeat a process in
| parallel and bam-ALU. From what I understand as a layperson,
| the size of the inputs is absolutely part of the scaling.
| dmurray wrote:
| But the reason factoring numbers is used as the quantum
| benchmark is exactly that we have a quantum algorithm for
| that problem which is meant to scale better than any known
| algorithm on a classical computer.
|
| So it seems like it takes an exponentially bigger device to
| factor 21 than 15, then 35 than 21, and so on, but if I
| understand right, at some point this levels out and it's
| only relatively speaking a little harder to factor say
| 10^30 than 10^29.
|
| Why are we so confident this is true given all of the
| experience so far trying to scale up from factoring 15 to
| factoring 21?
| bawolff wrote:
| > Why are we so confident this is true given all of the
| experience so far trying to scale up from factoring 15 to
| factoring 21?
|
| I don't think we have any "real" experience scaling from
| 15 to 21. Or at least not in the way shor's algorithm
| would be implemented in practise on fault tolerant
| qubits.
|
| We haven't even done 15 yet in a "real" way yet. I susect
| the amount of time to factor 15 on fault tolerant qubits
| will be a lot longer than the time to go from 15 to 21.
| pclmulqdq wrote:
| The algorithm in question is a hypothetical algorithm for
| a hypothetical computer with certain properties. The
| properties in question are assumed to be cheap.
|
| In the case of quantum algorithms in BQP, though, one of
| those properties is SNR of analog calculations (which is
| assumed to be infinite). SNR, as a general principle, is
| known to scale really poorly.
| bawolff wrote:
| > In the case of quantum algorithms in BQP, though, one
| of those properties is SNR of analog calculations (which
| is assumed to be infinite). SNR, as a general principle,
| is known to scale really poorly.
|
| As far as i understand, that isn't an assumption.
|
| The assumption is that the SNR of logical (error-
| corrected) qubits is near infinite, and that such logical
| qubits can be constructed from noisey physical qubits.
| pclmulqdq wrote:
| There are several properties that separate real quantum
| computers from the "BQP machine," including decoherence
| and SNR. Error-correction of qubits is mainly aimed at
| decoherence, but I'm not sure it really improves SNR of
| gates on logical qubits. SNR dictates how precisely you
| can manipulate the signal (these are a sort of weird kind
| of analog computer), and the QFTs involved in Shor's
| algorithm need some very precise rotations of qubits.
| Noise in the operation creates an error in that rotation
| angle. If your rotation is bad to begin with, I'm not
| sure the error correction actually helps.
| seanhunter wrote:
| > The assumption is that the SNR of logical (error-
| corrected) qubits is near infinite, and that such logical
| qubits can be constructed from noisey physical qubits.
|
| This is an argument I've heard before and I don't really
| understand it[1]. I get that you can make a logical qubit
| out of physical qubits and build in error correction so
| the logical qubit has perfect SNR, but surely if (say the
| number of physical qubits you need to get the nth logical
| qubit is O(n^2) for example, then the SNR (of the whole
| system) isn't near infinite it's really bad.
|
| [1] Which may well be because I don't understand quantum
| mechanics ...
| adgjlsfhk1 wrote:
| The really important thing is that logical qbit error
| decreases exponentially with error correction amount. As
| such, for the ~1000 qbit regime needed for factoring, the
| amount of error correction ends up being essentially a
| constant factor (~1000x physical to logical). As long as
| you can build enough "decent" quality physical qbits and
| connect them, you can get near perfect logical qbits.
| JanisErdmanis wrote:
| Having demonstrated error correction, some incremental
| improvements can now be made to make it more repeatable
| and with better characteristics.
|
| The hard problem then remains how to connect those qubits
| at scale. Using a coaxial cable for each qubit is
| impractical; some form of multiplexing is needed. This,
| in turn, causes qubits to decohere while waiting for
| their control signal.
| sfpotter wrote:
| The fact that it does appear to be so difficult to scale
| things up would suggest that the argument isn't silly.
| thrance wrote:
| Actually yes, how much numbers you can crunch per second and
| how big they are were among the first benchmarks for actual
| computers. Also, these prototypes were almost always
| immediately useful. (Think of the computer that cracked
| Enigma).
|
| In comparison, there is no realistic path forward for scaling
| quantum computers. Anyone serious that is not trying to sell
| you QC will tell you that quantum systems become
| exponentially less stable the bigger they are and the longer
| they live. That is a fundamental physical truth. And since
| they're still struggling to do _anything at all_ with a
| quantum computer, don 't get your hopes up too much.
| bawolff wrote:
| > Anyone serious that is not trying to sell you QC will
| tell you that quantum systems become exponentially less
| stable the bigger they are and the longer they live.
|
| If what you are saying is that error rates increase
| exponentially such that quantum error correction can never
| correct more errors than it introduces, i don't think that
| is a widely accepted position in the field.
| fragmede wrote:
| People who believed that would opt out of being in the
| field, though. No?
| amenhotep wrote:
| That would be the bombe, which didn't really crunch numbers
| at all, but was an electromechanical contraption to
| automate physically setting Enigma rotors to enumerate what
| combinations were possible matches.
| dboreham wrote:
| This is quite falatious and wrong. The first computers were
| built in order to solve problems immediately that were
| already being solved slowly by manual methods. There never
| was a period where people built computers so slow that they
| were slower than adding machines and slide rules, just
| because they seemed cool and might one day be much faster.
| bawolff wrote:
| Charles babbage started on the difference engine in 1819.
| It took a very long time after that before computers were
| useful.
| bawolff wrote:
| Additionally, part of the problem was that metal working
| at the time wasn't really advanced enough to make the
| required parts to the necessary precision at a reasonable
| price. Which sounds really quite similar to how modern
| quantum computers are right at the edge of current
| engineering technology.
| upofadown wrote:
| Perhaps? The sort of quantum computers that people are talking
| about now are not general purpose. So you might be able to make
| a useful quantum computer that is not Shor's algorithm.
| gsf_emergency_6 wrote:
| Simulating the Hubbard model for superconductors at large
| scales is significantly more likely to happen sooner than
| factoring RSA-2048 with Shor's algorithm.
|
| Google have been working on this for years
|
| Don't ask me if they've the top supercomputers beat, ask
| Gemini :)
| tomalbrc wrote:
| Gemini hallucinated me a wild answer.
| bawolff wrote:
| I don't think that's correct, the research projects the
| article is talking about all seem to aim at making general
| purpose quantum computers eventually. Obviously they haven't
| succeded yet, but general purpose does seem to be what they
| are talking about.
| Strilanc wrote:
| Factoring will be okay for tracking progress later; it's just a
| bad benchmark _now_. Factoring benchmarks have little
| visibility into fault tolerance spinning up, which is the
| important progress right now. Factoring becoming a reasonable
| benchmark is strongly related to quantum computing becoming
| useful.
| prof-dr-ir wrote:
| > Factoring becoming a reasonable benchmark is strongly
| related to quantum computing becoming useful.
|
| Either this relation is not _that_ strong, or factoring
| should "imminently" become a reasonable benchmark, or useful
| quantum computing cannot be "imminent". So which one is it?
|
| I think you are the author of the blogpost I linked to? Did I
| maybe interpret it too negatively, and was it not meant to
| suggest that the second option is still quite some time away?
| adgjlsfhk1 wrote:
| Under a Moore's law-like scenario, factoring 21 happens
| only about ~5 years before factoring a 1024 bit number.
| With all the optimizations, factoring an n bit number only
| requires ~n logical qbits, but most of those optimizations
| only work for large n, so 21 is only ~5 doubles away from
| 2^1024.
|
| the other problem is that factoring 21 is so easy that it
| actually makes it harder to prove you've factored it with a
| functional quantum computer. for big numbers, your program
| can fail 99% of the time because if you get the result
| once, you prove that the algorithm worked. 21 is small
| enough that it's hard not to factor, so demonstrating that
| you've factored it with a qc is fairly hard. I wouldn't be
| surprised as a result if the first number publicly factored
| by a quantum computer (using error correction) was in the
| thousands instead of 21. By using a number that is not
| absolutely tiny, it becomes a lot easier to show that the
| system works.
| bahmboo wrote:
| I particularly like the end of the post where he compares the
| history of nuclear fission to the progress on quantum computing.
| Traditional encryption might already be broken but we have not
| been told.
| bawolff wrote:
| In a world where spying on civilian communication of
| adversaries (and preventing spying on your own civilians) is
| becoming more critical for national security interests, i
| suspect that national governments would be lighting more of a
| fire if they believe their opponents had one.
| the8472 wrote:
| NSA _is_ pushing for PQ algos.
| mvkel wrote:
| They absolutely are. NSA is obsessed with post-quantum
| projects atm
| tyre wrote:
| But is this because they are already needed or because they
| want to preserve encryption for past and present data post-
| quantum?
| mvkel wrote:
| The latter
| GrilledChips wrote:
| tbh they could just be pushing for people to adopt newer,
| less-tested, weaker algorithms. switch from something
| battle-hardened to the QuantResist2000 algorithm which
| they've figured out how to break with lattice reduction and
| a couple of GPUs like those minecraft guys did.
| kibwen wrote:
| Hybrid approaches are at least as strong as their
| strongest algorithm. You don't need to trust me on this,
| it's extremely simple to derive this principle yourself
| from basic knowledge of cryptography.
| littlestymaar wrote:
| I really doubt we are anywhere close to this when there has
| been no published legit prime factorization beyond _21_ :
| https://eprint.iacr.org/2025/1237.pdf
|
| Surely if someone managed to factorize a 3 or 4 digits number,
| they would have published it as it's far enough of
| weaponization to be worth publishing. To be used to break
| cryptosystems, you need to be able to factor at least
| 2048-digits numbers. Even assuming the progress is linear with
| respect to the number of bits in the public key (this is the
| theoretical lower bound but assume hardware scaling is itself
| linear, which doesn't seem to be the case), there's a pretty
| big gap between 5 and 2048 and the fact that no-one has ever
| published any significant result (that is, not a magic trick by
| choosing the number in a way that makes the calculation
| trivial, see my link above) showing any process in that
| direction suggest we're not in any kind of immediate threat.
|
| The reality is that quantum computing is still very very hard,
| and very very far from being able what is theoretically
| possible with them.
| throw310822 wrote:
| So you have one of the scientists at the forefront of quantum
| computing theory telling you that he has no idea if quantum
| computing is already in a much more advanced state that he
| himself knows about?
|
| If results in quantum computing would start to "go dark",
| unpublished in scientific literature and only communicated to
| the government/ military, shouldn't he be one of the first to
| know or at least notice?
| ktallett wrote:
| As someone that works in quantum computing research both academic
| and private, no it isn't imminent in my understanding of the
| word, but it will happen. We are still at that point whereby we
| are comparable to 60's general computing development. Many
| different platforms and we have sort of decided on the best next
| step but we have many issues still to solve. A lot of the key
| issues have solutions, the problem is more getting everyone to
| focus in the right direction, which also will mean when funding
| starts to focus in the right direction. There are snake oil
| sellers right now and life will be imminently easier when they
| are removed.
| andsoitis wrote:
| > it will happen.
|
| If you were to guess what reasons there might be that it WON'T
| happen, what would some of those reasons be?
| ktallett wrote:
| So in my view, the issues I think about now are:
|
| - Too few researchers, as in my area of quantum computing. I
| would state there is one other group that has any academic
| rigour, and is actually making significant and important
| progress. The two other groups are using non reproducible
| results for credit and funding for private companies. You
| have FAANG style companies also doing research, and the
| research that comes out still is clearly for funding. It
| doesn't stand up under scrutiny of method (there usually
| isn't one although that will soon change as I am in the
| process of producing a recipe to get to the point we are
| currently at which is as far as anyone is at) and
| repeatability.
|
| - Too little progress. Now this is due to the research focus
| being spread too thin. We have currently the classic digital
| (qubit) vs analogue (photonic) quantum computing fight, and
| even within each we have such broad variations of where to
| focus. Therefore each category is still really just at the
| start as we are going in so many different directions. We
| aren't pooling our resources and trying to make progress
| together. This is also where a lack of openness regarding
| results and methods harms us. Likewise a lack of automation.
| Most significant research is done by human hand, which means
| building on it at a different research facility often
| requires learning off the person who developed the method in
| person if possible or at worse, just developing a method
| again which is a waste of time. If we don't see the results,
| the funding won't be there. Obviously classical computing
| eventually found a use case and then it became useful for the
| public but I fear we may not get to that stage as we may take
| too long.
|
| As an aside, we may also get to the stage whereby, it is
| useful but only in a military/security setting. I have worked
| on a security project (I was not bound by any NDA
| surprisingly but I'm still wary) featuring a quantum setup,
| that could of sorts be comparable to a single board computer
| (say of an ESP32), although much larger. There is some value
| to it, and that particular project could be implemented into
| security right now (I do not believe it has or will, I
| believe it was viability) and isn't that far off. But that
| particular project has no other uses, outside of the
| military/security.
| ecshafer wrote:
| Wouldn't the comparison be more like the 1920s for computing.
| We had useful working computers in the 1940s working on real
| problems doing what was not possible before hand. By the 1950s
| we had computers doing Nuclear bomb simulations and the 1960s
| we had computers in banks doing accounting and inventory. So we
| had computers by then, not in homes, but we had them. In the
| 1920s we had mechanical calculators and theories on computation
| emerging but not a general purpose computer. Until we have a
| quantum computer doing work at least at the level of a digital
| computer I can't really believe it being the 1960s.
| ktallett wrote:
| I'm not going to pretend that I am that knowledgeable on
| classic computing history from that time period. I was
| primarily going off the fact the semi conductor was built in
| the late 40's, and I would say we have the quantum version of
| that in both qubit and photonic based computing and they work
| and we have been developing on them for some time now. The
| key difference is that there are many more steps to get to
| the stage of making them useful. A transistor becamse useful
| extremely quickly and well in Quantum computing, these just
| haven't quite yet.
| tdeck wrote:
| Relay based electromechanical computers were doing real,
| practical work in the early 1940s.
| tokai wrote:
| Not to be snarky, but how is it comparable to 60's computing?
| There was a commercial market for computers and private and
| public sector adoption and use in the 60s.
| ktallett wrote:
| There is private sector adoption and planning now of specific
| single purpose focused quantum devices in military and
| security settings. They work and exist although I do not
| believe they are installed. I may be wrong on the exact date,
| as my classical computer knowledge isn't spot on. The point I
| was trying to make was that we have all the bits we need. We
| have the ability to make the photonic quantum version (which
| spoiler alert is where the focus needs to move to over the
| qubit method of quantum computing) of a transistor, so we
| have hit the 50's at least. The fundamentals at this point
| won't change. What will change is how they are put together
| and how they are made durable.
| layer8 wrote:
| What makes you confident that it will happen?
| mvkel wrote:
| The people who are inside the machine are usually the least
| qualified to predict the machine's future
| uejfiweun wrote:
| What an idiotic take. The LEAST qualified? Should I go ask
| some random junkie off the street where quantum computing
| will be in 5 years?
| charcircuit wrote:
| Yes. Apply wisdom of the crowd.
| GrilledChips wrote:
| In the 60's we actually had extremely capable, fully-developed
| computers. Advanced systems like the IBM System360 and CDC
| 6600.
|
| Quantum computing is currently stuck somewhere in the 1800's,
| when a lot of the theory was still being worked out and few
| functional devices had even been constructed.
| ktallett wrote:
| Oh no, that isn't factually correct. We have the theory. The
| theory is viable and provable and shown in both of the major
| branches of quantum computing, qubit and photonic. The key
| issue as I say is each has multiple 'architectures' for lack
| of a better term for each branch. We do have functional
| devices, it is just the function they provide is useless as
| we can already do it on a laptop. Which partially is a
| massive issue as Quantum computing almost needs to skip ahead
| of those development years classical computing was afforded.
| BlackFly wrote:
| Eh, quantum computing could very well be the next nuclear
| fusion where every couple of years forever each solved problem
| brings us to "We're 5 years away!"
|
| Yet, for sure we should keep funding both quantum computing and
| nuclear fusion research.
| noname120 wrote:
| What makes it more akin to 60's general computing development
| than 60's fusion power development (that is still ongoing!)?
| The former is incremental, the latter requires major
| technological breakthroughs before reaching any sort of
| usefulness. Quantum computing feels more like there are
| roadblocks that can't be ironed out without several
| technological revolutions.
| eightysixfour wrote:
| Did anyone else read the last two paragraphs as "I AM NOT ALLOWED
| TO TELL YOU THINGS YOU SHOULD BE VERY CONCERNED ABOUT" in bright
| flashing warning lights or is it just me?
| William_BB wrote:
| Just you
| ktallett wrote:
| It is more, many companies can't do what they claim to do, or
| they have done it once at best and had no more consistency. I
| sense most companies in the quantum computing space right now
| are of this ilk. As someone that works in academic and private
| quantum computing research, repeatability and methodology are
| severely lacking, which always rings alarm bells. Some
| companies are funded off the back of one very poor quality
| research paper, reviewed by people who are not experts, that
| then leads to a company that looks professional but behind the
| scenes I would imagine are saying Oh shit, now we actually have
| to do this thing we said we could do.
| bahmboo wrote:
| I don't think he is saying that. As I said in my other comment
| here I think he is just drawing a potential parallel to other
| historic work that was done in a private(secret) domain. The
| larger point is we simply don't know so it's best to act in a
| way that even if it hasn't been done already it certainly seems
| like it will be broken. Hence the move to Post-Quantum
| Cryptography is probably a good idea!
| griffzhowl wrote:
| Aaronson says:
|
| > This is the clearest warning that I can offer in public
| right now about the urgency of migrating to post-quantum
| cryptosystems...
|
| That has a clear implication that he knows something that he
| doesn't want to say publically
| machinationu wrote:
| a crypto system is expected to resist for 30 years.
|
| it doesnt need to be imminent for people to start moving
| now to post-quantum.
|
| if he thinks we are 10 years away from QC, we need to start
| moving now
| andrewflnr wrote:
| Very much so. But the specificity and severity of what he
| knows is not clear just from this. Not necessarily to the
| point of "bright flashing warning lights" as the top-level
| comment put it. Anyway, I certainly am glad that people are
| (as far as I can tell?) more or less on top of the post-
| quantum transition.
| griffzhowl wrote:
| Yes, it can easily just mean that he has some kind of
| inside information about progress that he doesn't want to
| divulge, but this is still far from "crypto is broken,
| guize"
|
| Still, if that's true, it's an example of the very thing
| Scott's talking about: there are advances in the field
| that aren't being made public.
| belter wrote:
| I ran it through ROT13, base64, reversed the bits, and then
| observed it....The act of decoding collapsed it into ...not
| imminent...
| svara wrote:
| He's making it sound that way, although he might plausibly deny
| that by claiming he just doesn't want to speculate publicly.
|
| Either way he must have known people would read it like you did
| when he wrote that; so we can safely assume it's boasting at
| the very least.
| tromp wrote:
| I realize this is a minority opinion, and goes against all
| theories of how quantum computing works, but I just cannot
| believe that nature will allow us to reliably compute with
| amplitudes as small as 2^-256. I still suspect something will
| break down as we approach and move below the planck scale.
| semi-extrinsic wrote:
| Fun fact: the Planck mass is about 22 micrograms, about the
| amount of Vitamin D in a typical multivitamin supplement, and
| the corresponding derived Planck momentum is 6.5 kg m/s, which
| is around how hard a child kicks a soccer ball. Nothing
| inherently special or limiting about these.
| ttoinou wrote:
| If you look at Planck units or any dimensionless set of
| physical units, you will see that mass stands apart from
| others units. There's like a factor 10^15 or something like
| this, i.e. we can't scale all physical units to be around the
| same values, something is going with mass and gravity that
| makes it different than others
| adrian_b wrote:
| After computing in 1899 for the first time the value of
| what is now named "Planck's constant" (despite the fact
| that Planck has computed both constants that are now named
| "Boltzmann's constant" and "Planck's constant"), Planck has
| immediately realized that this provides an extra value,
| besides those previously known, which can be used for the
| definition of a natural unit of measurement.
|
| Nevertheless, Planck did not understand well enough the
| requirements for a good system of fundamental units of
| measurement (because he was a theoretician, not an
| experimentalist; he had computed his constants by a better
| mathematical treatment of the experimental data provided by
| Paschen), so he did not find any good way to integrate
| Planck's constant in a system of fundamental units and he
| has made the same mistake made by Stoney 25 years before
| him (after computing the value of the elementary electric
| charge) and he has chosen the wrong method for defining the
| unit of mass among two variants previously proposed by
| Maxwell (the 2 variants were deriving the unit of mass from
| the mass of some atom or molecule and deriving the unit of
| mass from the Newtonian constant of gravitation).
|
| All dimensionless systems of fundamental units are
| worthless in practice (because they cause huge
| uncertainties in all values of absolute measurements) and
| they do not have any special theoretical significance (for
| now; such a significance would appear only if it became
| possible to compute exactly from theory the values of the 2
| constants of the electromagnetic interaction and
| gravitational interaction, instead of measuring them
| through experiments; until now nobody had any useful idea
| for a theory that could do such things).
|
| For the number of independently chosen fundamental units of
| measurement there exists an optimum value and the systems
| with either more or fewer fundamental units lead to greater
| uncertainties in the values of the physical quantities and
| to superfluous computations in the mathematical models.
|
| The dimensionless systems of units are not simpler, but
| more complicated, so attempting to eliminate the
| independently chosen fundamental units is the wrong goal
| when searching for the best system of units of measurement.
|
| My point is that the values of the so-called "Planck units"
| have absolutely no physical significance, therefore it is
| extremely wrong to use them in any reasoning about what is
| possible or impossible or about anything else.
|
| The "Planck units" are not unique, there also exists a very
| similar system of "Stoney units", proposed a quarter of
| century before the "Planck units", where the values of the
| units are different, and there are also other variants of
| dimensionless systems of units proposed later. None of them
| is better than the others and all are bad, the worst defect
| being that the huge experimental uncertainties from
| measuring the value of the Newtonian constant of
| gravitation are moved from that single value into the
| values of all unrelated physical quantities, so that no
| absolute value can be known precisely, but only the ratios
| between quantities of the same kind.
|
| In a useful system of fundamental units, for all units
| there are "natural" choices, except for one, which is the
| scale factor of the spatio-temporal units. For this scale
| factor of space-time, in the current state of knowledge
| there is no special value that can be distinguished from
| other arbitrary choices, so it is chosen solely based on
| the practical ease of building standards of frequency and
| wave-number that have adequate reproducibility and
| stability.
|
| The only historical value of the "Planck units" is that
| they provide a good example of how one should NOT choose a
| system of units of measurement. The fact that they are
| still frequently mentioned by some people in any other
| context than criticizing such a system just demonstrates
| the very sad state of physics education, where no physics
| textbook includes an adequate presentation of the
| foundation of physics, which is the theory of the
| measurement of physical quantities. One century and a half
| ago, Maxwell began his treatise on electricity and
| magnetism with a very good exposition of the state of
| metrology at that time, but later physics textbooks have
| become less and less rigorous, instead of improving.
| bawolff wrote:
| In some ways i think that is the most exciting possibility. If
| attempts at making quantum computers let us find exactly where
| the current theories break down and probe how that happens, it
| will probably be one of the most important physics discoveries
| of the century.
| krastanov wrote:
| The magnitude of an "amplitude" is basis dependent. A basis is
| a human invention, an arbitrary choice made by the human to
| describe nature. The choice of basis is not fundamental. So
| just choose a basis in which there are no vanishingly small
| amplitudes and your worry is addressed.
| oh_my_goodness wrote:
| 1/sqrt(N)
| tromp wrote:
| Any implementation of Shor will need vanishingly small
| amplitudes, as it forms a superposition of 2^256 classical
| states.
| jlokier wrote:
| The amplitudes aren't small in the 512-dimensional subspace
| where 256-qubit calculations take place.
|
| 2^256 states are comfortably distinct in that many dimensions
| with amplitude ~1. Their distinctness is entirely direction.
|
| The obvious parallels to vector embeddings and high-dimensional
| tensor properties have some groups working out how to combine
| them in "quantum AI", and because that doesn't require the same
| precision (like trained neurel nets still work usefully after
| heavy quantization and noise), quantum AI might arrive before
| regular quantum computation, and might be feasible even if the
| latter is not.
| Aardwolf wrote:
| Once quantum computers are possible, is there actually anything
| else, any other real world applications, besides breaking crypto
| and number theory problems that they can do, and do much better
| than regular computers?
| comicjk wrote:
| Yes, in fact they might be useful for chemistry simulation long
| before they are useful for cryptography. Simulations of quantum
| systems inherently scale better on quantum hardware.
|
| https://en.wikipedia.org/wiki/Quantum_computational_chemistr...
| GrilledChips wrote:
| More recently it's turned out that quantum computers are less
| useful for molecular simulation than previously thought. See:
| https://www.youtube.com/watch?v=pDj1QhPOVBo
|
| The video is essentially an argument from the software side
| (ironically she thinks the hardware side is going pretty
| well). Even if the hardware wasn't so hard to build or scale,
| there are surprisingly few problems where quantum algorithms
| have turned out to be useful.
| comicjk wrote:
| It is tough to beat classical computers. They work really
| well, and a huge amount of time (including some of mine)
| has gone into developing fast algorithms for them to do
| things they're not naturally fast at, such as quantum
| chemistry.
| oasisaimlessly wrote:
| At 15:00, she says "quantum computers are surprisingly good
| at [...] quantum simulations [of electron behavior]", which
| would seem to contradict you.
| smurda wrote:
| One theoretical use case is "Harvest Now, Decrypt Later" (HNDL)
| attacks, or "Store Now, Decrypt Later" (SNDL). If an oppressive
| regime saves encrypted messages now, they can decrypt later
| when QCs can break RSA and ECC.
|
| It's a good reason to implement post-quantum cryptography.
|
| Wasn't sure if you meant crypto (btc) or cryptography :)
| GrilledChips wrote:
| I will never get used to ECC meaning "Error Correcting Code"
| or "Elliptic Curve Cryptography." That said, this isn't
| unique to quantum expectations. Faster classical computers or
| better classical techniques could make various problems
| easier in the future.
| OJFord wrote:
| What do you want it to mean?
| silon42 wrote:
| I think he meant Error Correcting Code (just this, not
| this "or" ECCrypto)
| layer8 wrote:
| From TFA: 'One more time for those in the back: the main
| _known_ applications of quantum computers remain (1) the
| simulation of quantum physics and chemistry themselves, (2)
| breaking a lot of currently deployed cryptography, and (3)
| eventually, achieving some _modest_ benefits for optimization,
| machine learning, and other areas (but it will probably be a
| while before those modest benefits win out in practice). To be
| sure, the detailed list of quantum speedups expands over time
| (as new quantum algorithms get discovered) and also contracts
| over time (as some of the quantum algorithms get dequantized).
| But the list of known applications "from 30,000 feet" remains
| fairly close to what it was a quarter century ago, after you
| hack away the dense thickets of obfuscation and hype.'
| GrilledChips wrote:
| It turns out they're not so useful for chemistry.
| https://www.youtube.com/watch?v=pDj1QhPOVBo
| hattmall wrote:
| I believe the primary most practical use would be compression.
| Devices could have quantum decoder chips that give us massive
| compression gains which could also massively expand storage
| capacity. Even modest chips far before the realization of the
| scale necessary for cryptography breaking could give
| compression gains on the order of 100 to 1000x. IMO that's the
| real game changer. The theoretical modeling and cryptography
| breaking that you see papers being published on is much further
| out. The real work that isn't being publicized because of the
| importance of trade secrets is on storage / compression.
| Terr_ wrote:
| > compression gains on the order of 100 to 1000x.
|
| This feels like woo-woo to me.
|
| Suppose you're compressing the text of a book: How would a
| quantum processor let you get a much better compression
| ratio, even in theory?
|
| If you're mistakenly describing the density of information on
| some kind of physical object, that's not _data_ compression,
| that 's just a different storage medium.
| cubefox wrote:
| Pretty sure quantum algorithms can't be used for compression.
| askl wrote:
| Someone just has to figure out how to actually implement
| middle out compression on a quantum computer.
| tgi42 wrote:
| I worked in this field for years and helped build one of the
| recognizable companies. It has been disappointing to see, once
| again, promising science done in earnest be taken over by
| grifters. We knew many years ago that it was going to take FAR
| fewer qubits to crack encryption than pundits (and even experts)
| believed.
| jasonmarks_ wrote:
| Zero money take: quantum computing looks like a bunch of
| refrigerator companies.
|
| The fact that error correction seems to be struggling implies
| unaccounted for noise that is not heat. Who knows maybe
| gravitational waves heck your setup no matter what you do!
| willmadden wrote:
| We'll know when all of the old Bitcoin P2PK addresses and
| transacted from addresses are swept.
| GrilledChips wrote:
| the funny thing is that nobody will ever do that. The moment
| someone uses quantum computing or any other technology to crack
| bitcoin in a visible way, the coins they just gave to
| themselves become worthless because confidence collapses.
| pona-a wrote:
| There are some Bitcoin puzzles or old wallets that give some
| plausible deniability.
| Traubenfuchs wrote:
| Well, they wouldn't go for the trillion dollar wale
| addresses.
|
| They would hack random, long unused, dead addresses holding 5
| figure amounts and slowly convert those to money. They would
| eventually start to significantly lower the value and
| eventually crash bitcoin if too greedy, but could get filthy
| rich.
| Traubenfuchs wrote:
| Cloud providers will love it when we will need to buy more
| compute and memory for post quantum TSL.
| nacozarina wrote:
| another late signal will be a funding spike
|
| once someone makes a widget that extracts an RSA payload, their
| govt will seize, spend & scale
|
| they will try to keep it quiet but they will start a spending
| spree that will be visible from space
| cubefox wrote:
| This sounds slightly alarming:
|
| > I'm going to close this post with a warning. When Frisch and
| Peierls wrote their now-famous memo in March 1940, estimating the
| mass of Uranium-235 that would be needed for a fission bomb, they
| didn't publish it in a journal, but communicated the result
| through military channels only. As recently as February 1939,
| Frisch and Meitner had published in Nature their theoretical
| explanation of recent experiments, showing that the uranium
| nucleus could fission when bombarded by neutrons. But by 1940,
| Frisch and Peierls realized that the time for open publication of
| these matters had passed.
|
| > Similarly, at some point, the people doing detailed estimates
| of how many physical qubits and gates it'll take to break
| actually deployed cryptosystems using Shor's algorithm are going
| to stop publishing those estimates, if for no other reason than
| the risk of giving too much information to adversaries. Indeed,
| for all we know, that point may have been passed already. This is
| the clearest warning that I can offer in public right now about
| the urgency of migrating to post-quantum cryptosystems, a process
| that I'm grateful is already underway.
|
| Does anyone know how much underway it is? Do we need to worry
| that the switch away from RSA won't be broadly deployed before
| quantum decryption becomes available?
| JanisErdmanis wrote:
| From analytical arguments considering a rather generic error
| type, we already know that for the Shor algorithm to produce a
| useful result, the error rate with the number of logical qubits
| needs to decrease as ~n^(-1/3), where `n` is the number of bits
| in the number [1].
|
| This estimate, however, assumes that interaction can be turned
| on between arbitrary two qubits. In practice, we can only do
| nearest-neighbour interactions on a square lattice, and we need
| to simulate the interaction between two arbitrary qubits by
| repeated application of SWAP gates, mangling the interaction
| through as in the 15th puzzle. This two-qubit simulation would
| add about `n` SWAP gates, which would then multiply the noise
| factor by the same factor, hence now we need an error rate for
| logical qubits on a square lattice to be around ~n^(-4/3)
|
| Now comes the error correction. The estimates are somewhat hard
| to make here, as they depend on the sensitivity of the readout
| mechanism, but for example let's say a 10-bit number can be
| factored with a logical qubit error rate of 10^{-5}. Then we
| apply a surface code that scales exponentially, reducing the
| error rate by 10 times with 10 physical qubits, which we could
| express as ~1/10^{m/10}, where m is the number of physical
| qubits (which is rather optimistic). Putting in the numbers, it
| would follow that we need 40 physical qubits for a logical
| qubit, hence in total 400k physical qubits.
|
| That may sound reasonable, but then we made the assumption that
| while manipulating the individual physical qubits, decoherence
| for each individual qubit does not happen while they are
| waiting for their turn. This, in fact, scales poorly with the
| number of qubits on the chip because physical constraints limit
| the number of coaxial cables that can be attached, hence
| multiplexing of control signals and hence the waiting of the
| qubits is imminent. This waiting is even more pronounced in the
| quantum computer cluster proposals that tend to surface
| sometimes.
|
| [1]:
| https://link.springer.com/article/10.1007/s11432-023-3961-3
| osn9363739 wrote:
| This is the worst quantum computing will ever be.
| AlexandrB wrote:
| You assume no civilizational collapse is in our future.
| qgin wrote:
| Tbh this reply works for pretty much anything anyone ever
| says
| ktallett wrote:
| That vastly depends on if we choose to go in the right
| direction.
| noname120 wrote:
| I can't believe how the very first line of the article is a
| grotesque strawman. Tbh I expected better from Scott Aaronson.
| lukeasrodgers wrote:
| Could you elaborate as you why you think it is a grotesque
| strawman? It doesn't strike me as such, even on rereading.
| hiddencost wrote:
| The guy who spends most of his time posting either in favor of
| genocide or about how he got cancelled for being a misogynist?
| He's an excellent scientist but not a calm person.
| sallveburrpi wrote:
| So summary is that useful quantum computing is definitely not
| imminent (as in probably happening in the next 10-20 years) - or
| am I misreading ?
| ursAxZA wrote:
| Which one ends up being more accurate -- quantum-computing
| forecasts or fashion-magazine trend predictions?
| Antibabelic wrote:
| Is it possible that practical quantum computing is actually
| impossible and we only think it is because of our incomplete
| understanding of physics?
| yoan9224 wrote:
| Aaronson's take is characteristically grounded. The Willow chip
| announcement was impressive technically but the media coverage
| predictably overshot into "RSA is dead" territory when the actual
| achievement was improving error correction rates. The relevant
| timeline question is: when do quantum computers solve problems
| faster than classical computers for commercially useful tasks
| (not just contrived benchmarks)?
|
| The error correction milestone matters because it's the gate to
| scaling. Previous quantum systems had error rates that increased
| faster than you could add qubits, making large-scale quantum
| computing impossible. If Willow actually demonstrates below-
| threshold error rates at scale (I'd want independent
| verification), that unblocks the path to 1000+ logical qubit
| systems. But we're still probably 5-7 years from "useful quantum
| advantage" on problems like drug discovery or materials
| simulation.
|
| The economic argument is underrated. Even if quantum computers
| achieve theoretical advantage, they need to beat rapidly
| improving classical algorithms running on cheaper hardware. Every
| year we delay, classical GPUs get faster and quantum algorithms
| get optimized for near-term noisy hardware. The crossover point
| might be narrower than people expect.
|
| What I find fascinating is the potential for hybrid classical-
| quantum algorithms where quantum computers handle specific
| subroutines (like sampling from complex distributions or solving
| linear algebra problems) while classical computers do pre/post-
| processing. That's probably the first commercial application -
| not replacing classical computers entirely but augmenting them
| for specific bottlenecks. Imagine a drug discovery pipeline where
| the 3D protein folding simulation runs on quantum hardware but
| everything else is classical.
| OkayPhysicist wrote:
| First? Try only. I'd be willing to wager a _sizeable_ amount of
| money that no one save for a few niche research institutions
| trying to improve quantum computing will ever be using fully
| quantum setups.
|
| QC is not a panacea. There are a handful of algorithms that are
| in BQP-P, and most of those aren't really used in tasks I would
| imagine the average person frequently engaging in.
| Simultaneously, quantum computers necessarily have
| complications that classical computers lack. Combined, I doubt
| people will be using purely quantum computers ever.
| ProllyInfamous wrote:
| Vanderbilt University [0] is about to open a "quantum research
| graduate studies" campus, somewhere near Chattanooga, Tennessee.
|
| I have a degree in chemistry from that institution, and don't
| have a _clue_ what this means _beyond the $1,000,000,000 economic
| impact_ this facility is supposed to make upon our fair city,
| over the next decade.
|
| [*] <https://quantumzeitgeist.com/vanderbilt-university-
| quantum-q...>
|
| [0] In partnership with our government-subsidized "commercial
| quantum-ready" fiber network, EPB
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