15 ms·

Google claims to have proved its supremacy with new quantum computer

256 points by andrewstuart 3y ago

mikewarot 3y ago
The cited paper[1] references "random circuit sampling" which is defined in [2] which then gets so heavy into abstract math, and I give up. Can someone explain this in terms an EE or programmer can understand? [1] https://arxiv.org/abs/2304.11119 https://arxiv.org/abs/2304.11119 [2] https://arxiv.org/abs/2007.07872 https://arxiv.org/abs/2007.07872
- knorker 3y ago
  Like reddit's ELI5 (explain it like I'm five), but ELIHAM (explain it like I (only) have a masters)? Yeah, if someone could please do that.
- bob1029 3y ago
  > The theoretical basis for these experiments depends on sampling the output distributions of random quantum circuits; unfortunately, understanding how this theoretical basis can be used to define quantum supremacy is an extremely difficult task. Anyone attempting to understand how this sampling task relates to quantum supremacy must study concepts from random matrix theory, mathematical analysis, quantum chaos, computational complexity, and probability theory. Resources connecting these concepts in the context of quantum supremacy are scattered and often difficult to find. At the end of the day, people writing these papers are also human. The very same sorts of humans who pad resumes with shiny technology and self-serving complexity. This might be a case of a rabbit you do not want to chase.
  - Gravyness 3y ago
    > This might be a case of a rabbit you do not want to chase. I'm sure the researchers will all collectively realize this, if it were to be the case, and disregard their 12 year academic journey with their great salaries in favor of research into more important topics like world hunger, renewable energy, etc. I'm so sure that the percentage of sureness is an imaginary, quantum-entangled value between -7 and 13 billion percent.
    - junon 3y ago
      "academic journey" and "great salaries" generally don't go together.
    - cohomologo 3y ago
      I research QC. Feel free to explain how my skills could be used to meaningfully contribute to the problem of world hunger or renewable energy while also keeping me employed --- going back to college to train in a different field isn't feasible. If it's not so easy, then perhaps it's logical that QC researchers and AI researchers and software devs aren't all jumping ship to work on "more important topics"... You may just be spouting off, but I genuinely am asking. If someone else dissing QC research wants to make a pitch for a concrete plan on how to make a difference in the world with a physics PhD and years of experience in scientific computing, drop me a message.
- B1FF_PSUVM 3y ago
  > references "random circuit sampling" It's either Monte Carlo or bullshit.
  - canadianfella 3y ago
    [dead]
- swframe2 3y ago
  (I don't have a background (or interest) in quantum computing) I've tried some of the "chat with pdf" websites for other topics. It seems like they could help you understand the paper. If you give it a try, could you report back here on how it worked for you.
- pclmulqdq 3y ago
  > Can someone explain this in terms an EE or programmer can understand? Unfortunately not. The physicists who are behind quantum computing don't think the same way, and go straight for the abstract math to solve any problem. I am pretty sure they don't understand that most of our progress on computing up to this point is because you don't need to go into Galois fields or discrete math to describe what a computer or algorithm does. I'm also pretty sure that they don't know of another way to think about it.
  - OkayPhysicist 3y ago
    The second paper shared by the GP is actually just about as dumbed down as you can feasible get. The problem is that A) it uses some basic jargon, because it's fair to assume the only people interested in the result are people who understand the jargon and B) it's describing a completely impractical problem, designed to maximize the difference in performance between a quantum and classical computer rather than do anything particularly useful.
- pyentropy 3y ago
  Are you familiar with logic circuits (those made of gates like AND, OR, XOR, NAND)? Just like they are the founding blocks of classical computers, the founding block of quantum computers are quantum circuits. Quantum circuits are made of quantum logic gates like Hadamard, CNOT, Z, CZ, etc. Instead of bits as inputs and outputs, quantum logic gates have qubits. Unlike boolean logic where bits are 0 and 1, a qubit is a 2D vector [α β] where α and β are complex numbers, corresponding to a superposition of the zero and one bases: α * |0> + β * |1>. You can visualise a qubit as a point on a sphere, the so called Bloch sphere [1] There are multiple ways to implement a qubit, but you need to start with some quantum phenomenon. An example is the polarisation of a photon, so horizontal could be |0> and vertical polarisation could be |1> and the qubit is represented as complex vector of these two. If you've studied linear algebra you know manipulating a vector often involves linear transformations. Any linear transformation can be represented as a matrix - so applying gates is just doing matrix multiplication. Unary gates are 2x2 matrices and binary gates are 4x4 matrices - for photons they would be implemented with mirrors and optical waveplates. Measuring the polarisation at the end is the output. The output is not deterministic but it always follows the same distribution, so you could design a circuit that has |001> X% of the time, |010> Y%, |111> Z% of the time, etc. such that X + Y + Z + .. = 100%. I'm not too familiar with the details of random circuit sampling, but the idea is that you start with a big circuit that wasn't intentionally designed and therefore has no known properties we can exploit - instead it's a random mess of transformations to the qubits. A classical computer cannot run big quantum circuits - N gates with the 49 Google qubits requires like 2^49 * N^3 classical gates, so it won't be able to calculate the output distribution. However, what we can do is run the quantum circuit many times (do measurements on the quantum computer) and collect many samples. Given enough samples, a classical computer can verify whether there's consistency between them and whether an actual transformation produced them (and therefore quantum computation happened) or its just pure noise / garbage using cross entropy benchmarks [2]. Note that the purpose of the "random" in the random circuit is to introduce hardness and prevent cheating (assume that the classical computer is the "opponent" of the quantum computer); the circuits don't calculate anything useful / of human value. What's interesting is that once people with supercomputers saw the benchmark formula and analysed the constant factors, they found a loophole which let them run a classical algorithm which generates measurements/samples that satisfy the benchmark with 40K classical CPUs for a week, or even a single A100 within 140 days. Some of their success was due to the sheer power available and some is due to algorithmic cleverness (see: tensor networks). In my opinion, they are only disproving the Sycamore supremacy in a fussy way. [1] - https://en.wikipedia.org/wiki/Bloch_sphere https://en.wikipedia.org/wiki/Bloch_sphere [2] - https://en.wikipedia.org/wiki/Cross-entropy_benchmarking https://en.wikipedia.org/wiki/Cross-entropy_benchmarking
- OkayPhysicist 3y ago
  [2] is actually a phenomenally easy read for a physics paper, but it does assume an undergraduate physics degree's level of background. First, it's important to know that a quantum state (written as |letter>) is not directly observable. We can think of it as some vector, for which we can only apply an operation to to get out a scalar observable. A quantum circuit is a series of operations on a quantum state to create a different quantum state, which can be modeled as a matrix U, which is unitary (meaning U*U=1). The goal of "sampling a random quantum circuit" is trying to find the probability of observing some given observable if you keep applying random quantum circuits to a given input state.
taeric 3y ago
"This is a very nice demonstration of quantum advantage. While a great achievement academically, the algorithm used does not really have real world practical applications, though." Not having real world applications is not necessarily damning, of course. Curious to know what implications this has for general algorithms. Reading this, it almost makes it sound like there will be some algorithms that quantum is better at and that they won't necessarily be the same algorithms that "classical" computing uses.
- knorker 3y ago
  My understanding is that quantum computers only have two real use cases, as of today: 1. Breaking crypto. 2. Simulating other quantum systems. For (1) it's basically all downsides. For (2) unless you're a particle phycisist you'll never need quantum computers. But that's now. Maybe there will be a killer app for it some day, changing everything. Or indeed, we could get it indirectly. Maybe simulating quantum systems we could invent new battery technologies, which in turn changes our lives.
  - esrauch 3y ago
    If it is able to break crypto then surely that means it can do other "interesting" mathematical calculations that are currently extremely slow/hard though?
    - arcticbull 3y ago
      So far, to my knowledge, not faster than a classical system. We've been searching for decades for a problem with a better quantum solution than a classical solution, and it's been a tough slog. These are, at least thus far and from my limited perspective, very special-purpose accelerators. Shor's algorithm is the one thing that comes to mind tbh. "Breaking crypto" in this case isn't anything other than finding prime factors of an integer.
    - knorker 3y ago
      Possibly. This is way beyond my knowledge. But I'm not aware of many other "search this finite part of the number line for this property", where "this finite part" is still too big for classical computers. It almost sounds like quantum computers are tailor made for the types of problems we've been building cryptosystems on. But maybe this is not all quantum computers will be able to do. I couldn't even explain exactly how they apply to simulations of quantum systems, but have only taken more knowledgeable people at their word.
fsh 3y ago
Google's and IBM's previous "quantum supremacy" demonstrations were quickly crushed by improved classical simulations. Let's see if it survives this time.
- dataflow 3y ago
  Would you have any links handy for those?
- lbourdages 3y ago
  The main issue I had with their demonstrations were that the problems they chose were essentially "let's show that a quantum computer is better at being a quantum computer than a classical computer". Obviously they are, just like I'm better at being a human than ChatGPT is. I'm not saying they suck, but to proclaim that "quantum computers are superior" you need an actual use-case, IMO.
  - deleted 3y ago
    [deleted]
  - refulgentis 3y ago
    It's absolutely non-obvious, I'm dead serious. As far as I've understood keeping up over the years, there's a credible argument from a respected academic in the QC community that quantum computing is impossible.
    - lbourdages 3y ago
      Do you have a link handy? You've piqued my curiosity!
      - refulgentis 3y ago
        Here's an exhaustive covering: https://www.scottaaronson.com/democritus/lec14.html https://www.scottaaronson.com/democritus/lec14.html I would have picked it up in bits and pieces from blogs over years, here's an attempt to render that useful that is surely nitpickable: TL;DR: there's two types of caring about Google's claims of quantum supremacy: 1. HN tends to assume these articles are about breakthrough in _product usefulness_ and then tsk tsk about lack of impact. c.f. top comment currently gravely noting after reading the paper, its too noisy and a long way off. 2. The papers are about demonstrating _there is quantum computing at all_, the interest in the people in the know is about settling that question, the raw strongman feat isn't particularly interesting.
marricks 3y ago
> He said: “This is a very nice demonstration of quantum advantage. While a great achievement academically, the algorithm used does not really have real world practical applications, though. > “We really must get to utility quantum computing – an era where quantum computers with many thousand qubits actually begin to deliver value to society in a way that classical computers never will be able to.” This seems to be the most level headed take from the paper and an explanation why (if claims are to be believed) we haven't seen anything useful come from quantum computing yet that couldn't be done by classical computers. Maybe it still is all hype and the reason we haven't seen a useful calculation is because the only problems it can solve better than others happen to be especially contrived. I guess time will tell.
- tedivm 3y ago
  I don't think it's that the concepts are contrived (although the test cases certainly are), it's just that our quantum computers are really early in their development and can't do the more complicated things yet. It's like if we had calculators that took an hour to do each arithmetic operation- the fact that people wouldn't use it doesn't mean arithmetic is contrived, just that it isn't as powerful as better alternatives. As the quote mentions, we'll need "many thousand qubits" to reach the point where society itself is getting new benefits out of things. These contrived cases help figure out how to scale the whole system.
  - upofadown 3y ago
    It's more like if we had calculators that could not do any arithmetic operation at all... Someone someday might figure out how to make the calculator actually calculate, but not yet.
  - AbrahamParangi 3y ago
    There's a fundamental question as to whether or not it's exponentially difficult to add additional qubits. If each marginal qubit is 5% more difficult to add as the previous one the task would be essentially impossible - and even if it wasn't impossible it would turn out to basically be cheating (in that you would be doing exponential work via either the quantum computing route or the conventional route).
dataflow 3y ago
Dumb question: Say I have a wooden stick and I break it in half in less than a second. Assume a computer would need several minutes to simulate everything that would've happened in the stick. I clearly got the output faster than a computer (and with more precision), so does this imply I'm doing anything particularly fascinating? I assume the same scenario is possible to concoct for a quantum computer. I assume it wouldn't be particularly interesting either. So what are the criteria for distinguishing those scenarios from the "interesting" cases? And how do we know which case this one is like?
- bawolff 3y ago
  If you're in the stick making business and need to know how sticks break, the yes.
- deleted 3y ago
  [deleted]
- knorker 3y ago
  If you can control your experiment perfectly, then you don't need the simulation. Now break the wooden stick in half while on the moon. In space. At absolute zero. While under acceleration. While spinning. While bombarding it with 10^100 neutrinos/second. And do it with 100'000 randomized iterations of the wooden fibers.
- tedivm 3y ago
  I don't think this is a stupid question at all- it actually touches on some pretty interesting topics. The human brain is absolutely fascinating, in particular because it is extremely energy efficient and fast at the tasks it does. The more we learn and understand how the brain is working the more we'll be able to improve a ton of computer science topics, from AI to signals processing and a whole bunch more in between.
- jabbany 3y ago
  One would be the direction of entropy. Breaking the stick is not "particularly fascinating" because you're going in the direction of increasing entropy. However, _putting it back together_ is. In the simulation it takes no more effort to go one way or the other, while you probably cannot put the stick back together no matter how hard you tried. A quantum question that is "interesting" would also be similar to finding order out of disorder (e.g. factoring).
deleted 3y ago
[deleted]
jl6 3y ago
The ability to entangle particles feels like a really amazing new capability. (New in the last 100 years anyway). Like it’s a brand new kind of substance that has never been made before. Everything in all of history has been built out of boring old atoms, not these fancy new entangled things. Even if quantum computers turn out not to be able to solve interesting problems, I wonder if computers are the only thing we can make out of it.
- DonHopkins 3y ago
  Electric space heaters? That's crypto's most practical application.
  - oldgradstudent 3y ago
    Crypto makes extremely expensive space heaters. On the positive side, they are just as efficient as regular space heaters in producing heat from electricity.
  - rvz 3y ago
    Nope. That is now overtaken by AI (Especially LLMs), [0] which does not have any efficient methods of training, fine-tuning and inferencing. Crypto on the other hand has already has alternative consensus algorithms available today which can cut it emissions down significantly [1]. [0] https://gizmodo.com/chatgpt-ai-water-185000-gallons-training-nuclear-1850324249 https://gizmodo.com/chatgpt-ai-water-185000-gallons-training... [1] https://consensys.net/blog/press-release/ethereum-blockchain-eliminates-99-99-of-its-carbon-footprint-overnight-after-a-successful-merge-according-to-new-report/ https://consensys.net/blog/press-release/ethereum-blockchain...
- klyrs 3y ago
  Meh. They're just quasiparticles made out of bog standard particles.
snowstormsun 3y ago
Does someone know for reference how big of a number that computer can factor? Or some other complex problem that is not highly theoretical...
- adgjlsfhk1 3y ago
  Roughly 15 (all current attempts to factor bigger numbers cheat in various ways). The basic problem is that you need at least a thousand qbits to do anything remotely resembling useful (especially if you need any error correction).
hgl 3y ago
I wonder if Google is Xerox of our era, developing promising technologies only to be made practical and commercialized by other entities? Transformer is one example. Not sure if recent advancement in quantum computing is another.
sporkl 3y ago
I don't remember the details, but the reason the 2019 paper was challenged was because Google did not take into account quantum simulation optimization techniques when estimating how long the computation would run on classical computers. I wouldn't be surprised if there's a similar situation here, where unconsidered optimizations prevent this from being quantum advantage.
- oldgradstudent 3y ago
  The main challenge for the Google quantum supremacy result was that calling it a computer or what it does a computation never made any sense.
- klyrs 3y ago
  As I recall, they did not take the error rate into account. The result was dashed by somebody looking at their error rate and saying "we can compute that distribution to within 5%* with a classical computer." One would hope that they learned from this, but historically, supremacy claims have been rather short-lived. * number pulled out of a hat
oldgradstudent 3y ago
I'm sure it's faster than simulation, but in what sense is this a computer and in what sense is that a computation?
troupe 3y ago
The fact that the calculation would take 47 years on a classical computer is only a break through if the calculation is something we actually want to do. Otherwise it just means that we have created an unnecessary problem designed to be solved quickly by a quantum computer. That isn't to say that this quantum computer isn't impressive and a step forward. Just that the comparison isn't really meaningful unless the problem being calculated transcends computer architecture--meaning it is actually interesting to solve regardless of the architecture being used.
- tsimionescu 3y ago
  No one is claiming that general purpose quantum computers are useful right now. Instead, people are trying to prove that certain physical devices they have built behave like the theoretical model of a quantum computer. To help prove that, people have found contrived problems that don't care about errors but that theoretical quantum computers can solve exponentially faster than classical computers. If these physical devices can solve those problems, that is proof that they are on the right path to one day solving actually interesting problems like Shor's algorithm. There are of course some caveats. For one, the test problems discovered so far are believed to take exponentially more time on a classical computer, but there is no rigorous proof yet (in fact, it is not yet proven that there doesn't exist a classical algorithm that could run as fast as Shor's). The second is that the current quantum computers are so small compared to classical ones that, even with an exponential advantage, they can't always solve things fast enough to prove without a shadow of a doubt that they have this advantage. So, improvements in this time difference compared to the largest known classical computers is still a worthwhile goal.
pastelsky 3y ago
If I understand correctly, the limited amount of "expressiveness" a quantum computer has restricts its ability to solve useful problems. Couldn't you simply express useful problems as a function of problems that the quantum computer can already solve? Doing so might be extremely in-efficient, but give that there's so much performance leeway, it still might end up being similar to super computers of today?
squarefoot 3y ago
I know nothing about quantum computing, but when I read "does X instantly when rivals need 47 years", I immediately think about it being abused for brute forcing passwords and encryption keys. Would it be possible?
- EGreg 3y ago
  Why are you being downvotdx? We need to have way more discussion about this. The answer is — no one knows. In fact even classical computer algos might soon break modern crypto, especially Elliptic Curve crypto.
- Arch485 3y ago
  Not yet!
- kouru225 3y ago
  Government institutions have already been instructed to start using quantum computer safe encryption algorithms. Internationally, governments have been storing tons of encrypted data that they can’t currently decrypt because they expect to be able to decrypt it soon using quantum computers. There are already quantum computer safe encryption algorithms that have been released to the public. I don’t know exactly how they work, but one of them was about reverse engineering a path through multi-dimensional space. Expect SHA256 to disappear soon and be replaced.
  - return_to_monke 3y ago
    sha256 is a hash algo. you probably meant something else?
    - kouru225 3y ago
      Yea. I think maybe this is what happens when I read something I don’t fully understand but want to share the info. I think they’re switching their encryption algorithms and also they were looking into how quantum computing affects SHA256. Would have to find the article I was reading.
bradley13 3y ago
Seems like more of what we've seen: a quantum system is really good at...simulating a quantum system. Water us wet, whoopie.
DLA 3y ago
Can anyone recommend a few videos, papers, or books that "start at the beginning" for how quantum computing works--the physics parts like entanglement. I'm a computer scientist, so I'm good with the algorithm/programming aspects. Should I start with quantum annealing? Ideally I guess I'd like some pointers to good approachable resources on the ways qubits are made, maintained, written to and read from--start me off at the quantum version of the transistor. Thanks HN.
- cevi 3y ago
  This may be a bit on the theoretical side, but it's the best reference for quickly getting up to speed on how quantum computing and entanglement works that I know of: https://cs.uwaterloo.ca/~watrous/QC-notes/QC-notes.pdf https://cs.uwaterloo.ca/~watrous/QC-notes/QC-notes.pdf As for how actual physical qubits are maintained, that topic is tough to find a good explainer for, since every group has a different approach. Some groups use trapped ions, some use two-dimensional quasiparticles, some use spin states of photons... and no one has a clue which approach will be most practical in the end. It's analogous to not knowing whether clockwork or vacuum tubes will be the better way to implement a Turing machine.
deepburner 3y ago
Quantum Computing/Information researcher here. This article is largely garbage, the original (~2 month old) paper is surprisingly readable [0] and I suggest you to check it out. Here's my $0.02: The efforts of the Google team is commendable in that they're trying to squeeze as much out of their noisy systems as possible until error correction is here (they need to, to justify their existence after all) and they are aware of the shortcomings of the paradigm. But personally I don't see anything useful coming out until error correction and number of qubits are improved many orders of magnitude to have fault tolerant QC. The jury is still out on their utility once realized; Shor's algorithm is an obvious one followed by quantum simulation algorithms that might benefit chemistry and fundamental physics, but it's not as big of a silver bullet as we thought before for simulation. Maybe someone can tell me what fast prime factorization is good for besides breaking encryption. Also IBM released a paper[1] recently making similar claims ("quantum advantage without complete error correction") which got obliterated by 2 back to back papers [2,3] that did what they did for much cheaper on a classical computer. [0]: https://arxiv.org/pdf/2304.11119.pdf https://arxiv.org/pdf/2304.11119.pdf [1]: https://www.nature.com/articles/s41586-023-06096-3 https://www.nature.com/articles/s41586-023-06096-3 [2]: https://arxiv.org/pdf/2306.14887.pdf https://arxiv.org/pdf/2306.14887.pdf [3]: https://arxiv.org/pdf/2306.16372.pdf https://arxiv.org/pdf/2306.16372.pdf
- shawabawa3 3y ago
  > Maybe someone can tell me what fast prime factorization is good for besides breaking encryption. Maybe someone can tell me what alchemy is good for besides turning lead into gold?
  - Retric 3y ago
    Prime factorization only breaks a subset of crypto algorithms, it’s not that useful or game changing alone.
  - NooneAtAll3 3y ago
    considering that the world is transitioning to post-quantum crypto... everyone moved from gold to digital currencies, pretty much
gigel82 3y ago
So it can generate lots of random numbers very fast... cool. /s
mabbo 3y ago
I feel like quantum computing is one of those technologies that is going to be a lot of hype and excitement by researchers, but no real applications and no real impact to the general public. ... Until the day that it does. And then, a lot of very interesting things will happen very quickly, and the world will change massively.
sixQuarks 3y ago
Imagine trying to explain this article to a caveman, or even someone from 200 years ago.
superposeur 3y ago
Do you know if there are any arguments in the literature to the effect that actually useful quantum supremacy may never be possible in principle (not merely in practice)? What I mean is: decoherence with environment must be held at bay long enough for the final answer to appear in the qubits with high probability. Based on examples from thermodynamics (such as impossibility of extracting useful work from a heat reservoir without a second, lower-temperature reservoir into which to dump heat), I could imagine a scenario where decoherence would always foil the computation at some point, perhaps at some intermediate time or in the final measurement. In particular examples, this would show up as irksome experimental limitations, but in fact these limitations would all stem from a deeper prohibition. And to the extent that decoherence could be managed (such as in the cited experiment), the resulting computation would not be "useful".
dekhn 3y ago
the best thing about watching the entire quantum computing debacle is every time somebody says their QC does something faster than a classical computer, somebody tunes the classical computer to beat the QC. Combined with the fact that chip infrastructure is already paid for and there is a large market to enable economy of scale, coupled with the lack of true problems where exponentially better problem solving is critical to business or military success, means we're going to see a series of QC claims that really just prop up classical computers for some time. (I used to work in supercomputing and chemistry and await the day we have useful QCs doing simulation better than what we can do on supercomputers)
- pclmulqdq 3y ago
  With all of the sensationalization, I am now convinced that many of the people in quantum computing itself are grifters, and that funding agencies keep paying them to put pressure on classical computing (despite knowing that QC is a big grift). Already, optimization problems have seen classical "ising" chips get great results (as good as the quantum annealing chips), proving that optimization doesn't actually need tunneling or superposition. Now, the number theorists just need to come up with a classical analog for a QFT or another similar transform, and we will see them obviate QC here. Arguably, RSA being obsolete has already done this. In simulation, supercomputers are also making huge advances in power.
  - bawolff 3y ago
    When people are hyping something that is probably still 20 years out, i think its safe to say they are trying to sell you something. Quantum computers will be a real (albeit not earth shattering) advance, but we are still far off. Still rather people pump money here than crypto bs.
    - pclmulqdq 3y ago
      Quantum computing has been 10 years away for the last 30 years.
moonshadow565 3y ago
How exactly does this make their search engine better?
- cbsmith 3y ago
  You forget that their real business is ads.
m3kw9 3y ago
So this is similar to the FizzBuzz post where they are trying to make an algorithm to make it the fastest, but really is useless.
neonate 3y ago
https://archive.md/T6viH https://archive.md/T6viH
jscipione 3y ago
Quantum computers make it practical for us to solve problems at much faster speeds, but at what cost? Quantum computers change the quantum state of particles in parallel universes, and likewise quantum computers in other universes change the quantum state of particles in our Universe. What is the effect of this? We should expect to see random otherwise unexplainable changes, and that’s exactly what we’ve seen over the last 10 years, it’s called the “Mandela Effect.” But despite the name referring to an important historic figure most “mandela effects” are tiny almost insignificant changes such as the spelling of The Bernstein Bears or the presence of a Cornucopia in Fruit of the Loom logo, the kind of thing that quantum changes could alter. I realize this is probably too far out there for most Hacker News readers and I’ll get down-voted for it, but I believe there may be a real danger here, and it’s something we need to watch out for as we develop quantum computers further. If we don’t take the threat seriously the Universe we live in now may become different from the one we remember, and we will need to provide safe-guards to retain the consistency of our Universe.

256 points by andrewstuart 3y ago

The cited paper[1] references "random circuit sampling" which is defined in [2] which then gets so heavy into abstract math, and I give up. Can someone explain this in terms an EE or programmer can understand? [1] https://arxiv.org/abs/2304.11119 https://arxiv.org/abs/2304.11119 [2] https://arxiv.org/abs/2007.07872 https://arxiv.org/abs/2007.07872

knorker 3y ago
Like reddit's ELI5 (explain it like I'm five), but ELIHAM (explain it like I (only) have a masters)? Yeah, if someone could please do that.
bob1029 3y ago
> The theoretical basis for these experiments depends on sampling the output distributions of random quantum circuits; unfortunately, understanding how this theoretical basis can be used to define quantum supremacy is an extremely difficult task. Anyone attempting to understand how this sampling task relates to quantum supremacy must study concepts from random matrix theory, mathematical analysis, quantum chaos, computational complexity, and probability theory. Resources connecting these concepts in the context of quantum supremacy are scattered and often difficult to find. At the end of the day, people writing these papers are also human. The very same sorts of humans who pad resumes with shiny technology and self-serving complexity. This might be a case of a rabbit you do not want to chase.
- Gravyness 3y ago
  > This might be a case of a rabbit you do not want to chase. I'm sure the researchers will all collectively realize this, if it were to be the case, and disregard their 12 year academic journey with their great salaries in favor of research into more important topics like world hunger, renewable energy, etc. I'm so sure that the percentage of sureness is an imaginary, quantum-entangled value between -7 and 13 billion percent.
  - junon 3y ago
    "academic journey" and "great salaries" generally don't go together.
  - cohomologo 3y ago
    I research QC. Feel free to explain how my skills could be used to meaningfully contribute to the problem of world hunger or renewable energy while also keeping me employed --- going back to college to train in a different field isn't feasible. If it's not so easy, then perhaps it's logical that QC researchers and AI researchers and software devs aren't all jumping ship to work on "more important topics"... You may just be spouting off, but I genuinely am asking. If someone else dissing QC research wants to make a pitch for a concrete plan on how to make a difference in the world with a physics PhD and years of experience in scientific computing, drop me a message.
B1FF_PSUVM 3y ago
> references "random circuit sampling" It's either Monte Carlo or bullshit.
- canadianfella 3y ago
  [dead]
swframe2 3y ago
(I don't have a background (or interest) in quantum computing) I've tried some of the "chat with pdf" websites for other topics. It seems like they could help you understand the paper. If you give it a try, could you report back here on how it worked for you.
pclmulqdq 3y ago
> Can someone explain this in terms an EE or programmer can understand? Unfortunately not. The physicists who are behind quantum computing don't think the same way, and go straight for the abstract math to solve any problem. I am pretty sure they don't understand that most of our progress on computing up to this point is because you don't need to go into Galois fields or discrete math to describe what a computer or algorithm does. I'm also pretty sure that they don't know of another way to think about it.
- OkayPhysicist 3y ago
  The second paper shared by the GP is actually just about as dumbed down as you can feasible get. The problem is that A) it uses some basic jargon, because it's fair to assume the only people interested in the result are people who understand the jargon and B) it's describing a completely impractical problem, designed to maximize the difference in performance between a quantum and classical computer rather than do anything particularly useful.
pyentropy 3y ago
Are you familiar with logic circuits (those made of gates like AND, OR, XOR, NAND)? Just like they are the founding blocks of classical computers, the founding block of quantum computers are quantum circuits. Quantum circuits are made of quantum logic gates like Hadamard, CNOT, Z, CZ, etc. Instead of bits as inputs and outputs, quantum logic gates have qubits. Unlike boolean logic where bits are 0 and 1, a qubit is a 2D vector [α β] where α and β are complex numbers, corresponding to a superposition of the zero and one bases: α * |0> + β * |1>. You can visualise a qubit as a point on a sphere, the so called Bloch sphere [1] There are multiple ways to implement a qubit, but you need to start with some quantum phenomenon. An example is the polarisation of a photon, so horizontal could be |0> and vertical polarisation could be |1> and the qubit is represented as complex vector of these two. If you've studied linear algebra you know manipulating a vector often involves linear transformations. Any linear transformation can be represented as a matrix - so applying gates is just doing matrix multiplication. Unary gates are 2x2 matrices and binary gates are 4x4 matrices - for photons they would be implemented with mirrors and optical waveplates. Measuring the polarisation at the end is the output. The output is not deterministic but it always follows the same distribution, so you could design a circuit that has |001> X% of the time, |010> Y%, |111> Z% of the time, etc. such that X + Y + Z + .. = 100%. I'm not too familiar with the details of random circuit sampling, but the idea is that you start with a big circuit that wasn't intentionally designed and therefore has no known properties we can exploit - instead it's a random mess of transformations to the qubits. A classical computer cannot run big quantum circuits - N gates with the 49 Google qubits requires like 2^49 * N^3 classical gates, so it won't be able to calculate the output distribution. However, what we can do is run the quantum circuit many times (do measurements on the quantum computer) and collect many samples. Given enough samples, a classical computer can verify whether there's consistency between them and whether an actual transformation produced them (and therefore quantum computation happened) or its just pure noise / garbage using cross entropy benchmarks [2]. Note that the purpose of the "random" in the random circuit is to introduce hardness and prevent cheating (assume that the classical computer is the "opponent" of the quantum computer); the circuits don't calculate anything useful / of human value. What's interesting is that once people with supercomputers saw the benchmark formula and analysed the constant factors, they found a loophole which let them run a classical algorithm which generates measurements/samples that satisfy the benchmark with 40K classical CPUs for a week, or even a single A100 within 140 days. Some of their success was due to the sheer power available and some is due to algorithmic cleverness (see: tensor networks). In my opinion, they are only disproving the Sycamore supremacy in a fussy way. [1] - https://en.wikipedia.org/wiki/Bloch_sphere https://en.wikipedia.org/wiki/Bloch_sphere [2] - https://en.wikipedia.org/wiki/Cross-entropy_benchmarking https://en.wikipedia.org/wiki/Cross-entropy_benchmarking
OkayPhysicist 3y ago
[2] is actually a phenomenally easy read for a physics paper, but it does assume an undergraduate physics degree's level of background. First, it's important to know that a quantum state (written as |letter>) is not directly observable. We can think of it as some vector, for which we can only apply an operation to to get out a scalar observable. A quantum circuit is a series of operations on a quantum state to create a different quantum state, which can be modeled as a matrix U, which is unitary (meaning U*U=1). The goal of "sampling a random quantum circuit" is trying to find the probability of observing some given observable if you keep applying random quantum circuits to a given input state.

taeric 3y ago

"This is a very nice demonstration of quantum advantage. While a great achievement academically, the algorithm used does not really have real world practical applications, though." Not having real world applications is not necessarily damning, of course. Curious to know what implications this has for general algorithms. Reading this, it almost makes it sound like there will be some algorithms that quantum is better at and that they won't necessarily be the same algorithms that "classical" computing uses.

knorker 3y ago
My understanding is that quantum computers only have two real use cases, as of today: 1. Breaking crypto. 2. Simulating other quantum systems. For (1) it's basically all downsides. For (2) unless you're a particle phycisist you'll never need quantum computers. But that's now. Maybe there will be a killer app for it some day, changing everything. Or indeed, we could get it indirectly. Maybe simulating quantum systems we could invent new battery technologies, which in turn changes our lives.
- esrauch 3y ago
  If it is able to break crypto then surely that means it can do other "interesting" mathematical calculations that are currently extremely slow/hard though?
  - arcticbull 3y ago
    So far, to my knowledge, not faster than a classical system. We've been searching for decades for a problem with a better quantum solution than a classical solution, and it's been a tough slog. These are, at least thus far and from my limited perspective, very special-purpose accelerators. Shor's algorithm is the one thing that comes to mind tbh. "Breaking crypto" in this case isn't anything other than finding prime factors of an integer.
  - knorker 3y ago
    Possibly. This is way beyond my knowledge. But I'm not aware of many other "search this finite part of the number line for this property", where "this finite part" is still too big for classical computers. It almost sounds like quantum computers are tailor made for the types of problems we've been building cryptosystems on. But maybe this is not all quantum computers will be able to do. I couldn't even explain exactly how they apply to simulations of quantum systems, but have only taken more knowledgeable people at their word.

fsh 3y ago

Google's and IBM's previous "quantum supremacy" demonstrations were quickly crushed by improved classical simulations. Let's see if it survives this time.

dataflow 3y ago
Would you have any links handy for those?
lbourdages 3y ago
The main issue I had with their demonstrations were that the problems they chose were essentially "let's show that a quantum computer is better at being a quantum computer than a classical computer". Obviously they are, just like I'm better at being a human than ChatGPT is. I'm not saying they suck, but to proclaim that "quantum computers are superior" you need an actual use-case, IMO.
- deleted 3y ago
  [deleted]
- refulgentis 3y ago
  It's absolutely non-obvious, I'm dead serious. As far as I've understood keeping up over the years, there's a credible argument from a respected academic in the QC community that quantum computing is impossible.
  - lbourdages 3y ago
    Do you have a link handy? You've piqued my curiosity!
    - refulgentis 3y ago
      Here's an exhaustive covering: https://www.scottaaronson.com/democritus/lec14.html https://www.scottaaronson.com/democritus/lec14.html I would have picked it up in bits and pieces from blogs over years, here's an attempt to render that useful that is surely nitpickable: TL;DR: there's two types of caring about Google's claims of quantum supremacy: 1. HN tends to assume these articles are about breakthrough in _product usefulness_ and then tsk tsk about lack of impact. c.f. top comment currently gravely noting after reading the paper, its too noisy and a long way off. 2. The papers are about demonstrating _there is quantum computing at all_, the interest in the people in the know is about settling that question, the raw strongman feat isn't particularly interesting.

marricks 3y ago

> He said: “This is a very nice demonstration of quantum advantage. While a great achievement academically, the algorithm used does not really have real world practical applications, though. > “We really must get to utility quantum computing – an era where quantum computers with many thousand qubits actually begin to deliver value to society in a way that classical computers never will be able to.” This seems to be the most level headed take from the paper and an explanation why (if claims are to be believed) we haven't seen anything useful come from quantum computing yet that couldn't be done by classical computers. Maybe it still is all hype and the reason we haven't seen a useful calculation is because the only problems it can solve better than others happen to be especially contrived. I guess time will tell.

tedivm 3y ago
I don't think it's that the concepts are contrived (although the test cases certainly are), it's just that our quantum computers are really early in their development and can't do the more complicated things yet. It's like if we had calculators that took an hour to do each arithmetic operation- the fact that people wouldn't use it doesn't mean arithmetic is contrived, just that it isn't as powerful as better alternatives. As the quote mentions, we'll need "many thousand qubits" to reach the point where society itself is getting new benefits out of things. These contrived cases help figure out how to scale the whole system.
- upofadown 3y ago
  It's more like if we had calculators that could not do any arithmetic operation at all... Someone someday might figure out how to make the calculator actually calculate, but not yet.
- AbrahamParangi 3y ago
  There's a fundamental question as to whether or not it's exponentially difficult to add additional qubits. If each marginal qubit is 5% more difficult to add as the previous one the task would be essentially impossible - and even if it wasn't impossible it would turn out to basically be cheating (in that you would be doing exponential work via either the quantum computing route or the conventional route).

dataflow 3y ago

Dumb question: Say I have a wooden stick and I break it in half in less than a second. Assume a computer would need several minutes to simulate everything that would've happened in the stick. I clearly got the output faster than a computer (and with more precision), so does this imply I'm doing anything particularly fascinating? I assume the same scenario is possible to concoct for a quantum computer. I assume it wouldn't be particularly interesting either. So what are the criteria for distinguishing those scenarios from the "interesting" cases? And how do we know which case this one is like?

bawolff 3y ago
If you're in the stick making business and need to know how sticks break, the yes.
deleted 3y ago
[deleted]
knorker 3y ago
If you can control your experiment perfectly, then you don't need the simulation. Now break the wooden stick in half while on the moon. In space. At absolute zero. While under acceleration. While spinning. While bombarding it with 10^100 neutrinos/second. And do it with 100'000 randomized iterations of the wooden fibers.
tedivm 3y ago
I don't think this is a stupid question at all- it actually touches on some pretty interesting topics. The human brain is absolutely fascinating, in particular because it is extremely energy efficient and fast at the tasks it does. The more we learn and understand how the brain is working the more we'll be able to improve a ton of computer science topics, from AI to signals processing and a whole bunch more in between.
jabbany 3y ago
One would be the direction of entropy. Breaking the stick is not "particularly fascinating" because you're going in the direction of increasing entropy. However, _putting it back together_ is. In the simulation it takes no more effort to go one way or the other, while you probably cannot put the stick back together no matter how hard you tried. A quantum question that is "interesting" would also be similar to finding order out of disorder (e.g. factoring).

deleted 3y ago

[deleted]

jl6 3y ago

The ability to entangle particles feels like a really amazing new capability. (New in the last 100 years anyway). Like it’s a brand new kind of substance that has never been made before. Everything in all of history has been built out of boring old atoms, not these fancy new entangled things. Even if quantum computers turn out not to be able to solve interesting problems, I wonder if computers are the only thing we can make out of it.

DonHopkins 3y ago
Electric space heaters? That's crypto's most practical application.
- oldgradstudent 3y ago
  Crypto makes extremely expensive space heaters. On the positive side, they are just as efficient as regular space heaters in producing heat from electricity.
- rvz 3y ago
  Nope. That is now overtaken by AI (Especially LLMs), [0] which does not have any efficient methods of training, fine-tuning and inferencing. Crypto on the other hand has already has alternative consensus algorithms available today which can cut it emissions down significantly [1]. [0] https://gizmodo.com/chatgpt-ai-water-185000-gallons-training-nuclear-1850324249 https://gizmodo.com/chatgpt-ai-water-185000-gallons-training... [1] https://consensys.net/blog/press-release/ethereum-blockchain-eliminates-99-99-of-its-carbon-footprint-overnight-after-a-successful-merge-according-to-new-report/ https://consensys.net/blog/press-release/ethereum-blockchain...
klyrs 3y ago
Meh. They're just quasiparticles made out of bog standard particles.

snowstormsun 3y ago

Does someone know for reference how big of a number that computer can factor? Or some other complex problem that is not highly theoretical...

adgjlsfhk1 3y ago
Roughly 15 (all current attempts to factor bigger numbers cheat in various ways). The basic problem is that you need at least a thousand qbits to do anything remotely resembling useful (especially if you need any error correction).

hgl 3y ago

I wonder if Google is Xerox of our era, developing promising technologies only to be made practical and commercialized by other entities? Transformer is one example. Not sure if recent advancement in quantum computing is another.

sporkl 3y ago

I don't remember the details, but the reason the 2019 paper was challenged was because Google did not take into account quantum simulation optimization techniques when estimating how long the computation would run on classical computers. I wouldn't be surprised if there's a similar situation here, where unconsidered optimizations prevent this from being quantum advantage.

oldgradstudent 3y ago
The main challenge for the Google quantum supremacy result was that calling it a computer or what it does a computation never made any sense.
klyrs 3y ago
As I recall, they did not take the error rate into account. The result was dashed by somebody looking at their error rate and saying "we can compute that distribution to within 5%* with a classical computer." One would hope that they learned from this, but historically, supremacy claims have been rather short-lived. * number pulled out of a hat

oldgradstudent 3y ago

I'm sure it's faster than simulation, but in what sense is this a computer and in what sense is that a computation?

troupe 3y ago

The fact that the calculation would take 47 years on a classical computer is only a break through if the calculation is something we actually want to do. Otherwise it just means that we have created an unnecessary problem designed to be solved quickly by a quantum computer. That isn't to say that this quantum computer isn't impressive and a step forward. Just that the comparison isn't really meaningful unless the problem being calculated transcends computer architecture--meaning it is actually interesting to solve regardless of the architecture being used.

tsimionescu 3y ago
No one is claiming that general purpose quantum computers are useful right now. Instead, people are trying to prove that certain physical devices they have built behave like the theoretical model of a quantum computer. To help prove that, people have found contrived problems that don't care about errors but that theoretical quantum computers can solve exponentially faster than classical computers. If these physical devices can solve those problems, that is proof that they are on the right path to one day solving actually interesting problems like Shor's algorithm. There are of course some caveats. For one, the test problems discovered so far are believed to take exponentially more time on a classical computer, but there is no rigorous proof yet (in fact, it is not yet proven that there doesn't exist a classical algorithm that could run as fast as Shor's). The second is that the current quantum computers are so small compared to classical ones that, even with an exponential advantage, they can't always solve things fast enough to prove without a shadow of a doubt that they have this advantage. So, improvements in this time difference compared to the largest known classical computers is still a worthwhile goal.

pastelsky 3y ago

If I understand correctly, the limited amount of "expressiveness" a quantum computer has restricts its ability to solve useful problems. Couldn't you simply express useful problems as a function of problems that the quantum computer can already solve? Doing so might be extremely in-efficient, but give that there's so much performance leeway, it still might end up being similar to super computers of today?

squarefoot 3y ago

I know nothing about quantum computing, but when I read "does X instantly when rivals need 47 years", I immediately think about it being abused for brute forcing passwords and encryption keys. Would it be possible?

EGreg 3y ago
Why are you being downvotdx? We need to have way more discussion about this. The answer is — no one knows. In fact even classical computer algos might soon break modern crypto, especially Elliptic Curve crypto.
Arch485 3y ago
Not yet!
kouru225 3y ago
Government institutions have already been instructed to start using quantum computer safe encryption algorithms. Internationally, governments have been storing tons of encrypted data that they can’t currently decrypt because they expect to be able to decrypt it soon using quantum computers. There are already quantum computer safe encryption algorithms that have been released to the public. I don’t know exactly how they work, but one of them was about reverse engineering a path through multi-dimensional space. Expect SHA256 to disappear soon and be replaced.
- return_to_monke 3y ago
  sha256 is a hash algo. you probably meant something else?
  - kouru225 3y ago
    Yea. I think maybe this is what happens when I read something I don’t fully understand but want to share the info. I think they’re switching their encryption algorithms and also they were looking into how quantum computing affects SHA256. Would have to find the article I was reading.

bradley13 3y ago

Seems like more of what we've seen: a quantum system is really good at...simulating a quantum system. Water us wet, whoopie.

DLA 3y ago

Can anyone recommend a few videos, papers, or books that "start at the beginning" for how quantum computing works--the physics parts like entanglement. I'm a computer scientist, so I'm good with the algorithm/programming aspects. Should I start with quantum annealing? Ideally I guess I'd like some pointers to good approachable resources on the ways qubits are made, maintained, written to and read from--start me off at the quantum version of the transistor. Thanks HN.

cevi 3y ago
This may be a bit on the theoretical side, but it's the best reference for quickly getting up to speed on how quantum computing and entanglement works that I know of: https://cs.uwaterloo.ca/~watrous/QC-notes/QC-notes.pdf https://cs.uwaterloo.ca/~watrous/QC-notes/QC-notes.pdf As for how actual physical qubits are maintained, that topic is tough to find a good explainer for, since every group has a different approach. Some groups use trapped ions, some use two-dimensional quasiparticles, some use spin states of photons... and no one has a clue which approach will be most practical in the end. It's analogous to not knowing whether clockwork or vacuum tubes will be the better way to implement a Turing machine.

deepburner 3y ago

Quantum Computing/Information researcher here. This article is largely garbage, the original (~2 month old) paper is surprisingly readable [0] and I suggest you to check it out. Here's my $0.02: The efforts of the Google team is commendable in that they're trying to squeeze as much out of their noisy systems as possible until error correction is here (they need to, to justify their existence after all) and they are aware of the shortcomings of the paradigm. But personally I don't see anything useful coming out until error correction and number of qubits are improved many orders of magnitude to have fault tolerant QC. The jury is still out on their utility once realized; Shor's algorithm is an obvious one followed by quantum simulation algorithms that might benefit chemistry and fundamental physics, but it's not as big of a silver bullet as we thought before for simulation. Maybe someone can tell me what fast prime factorization is good for besides breaking encryption. Also IBM released a paper[1] recently making similar claims ("quantum advantage without complete error correction") which got obliterated by 2 back to back papers [2,3] that did what they did for much cheaper on a classical computer. [0]: https://arxiv.org/pdf/2304.11119.pdf https://arxiv.org/pdf/2304.11119.pdf [1]: https://www.nature.com/articles/s41586-023-06096-3 https://www.nature.com/articles/s41586-023-06096-3 [2]: https://arxiv.org/pdf/2306.14887.pdf https://arxiv.org/pdf/2306.14887.pdf [3]: https://arxiv.org/pdf/2306.16372.pdf https://arxiv.org/pdf/2306.16372.pdf

shawabawa3 3y ago
> Maybe someone can tell me what fast prime factorization is good for besides breaking encryption. Maybe someone can tell me what alchemy is good for besides turning lead into gold?
- Retric 3y ago
  Prime factorization only breaks a subset of crypto algorithms, it’s not that useful or game changing alone.
- NooneAtAll3 3y ago
  considering that the world is transitioning to post-quantum crypto... everyone moved from gold to digital currencies, pretty much

gigel82 3y ago

So it can generate lots of random numbers very fast... cool. /s

mabbo 3y ago

I feel like quantum computing is one of those technologies that is going to be a lot of hype and excitement by researchers, but no real applications and no real impact to the general public. ... Until the day that it does. And then, a lot of very interesting things will happen very quickly, and the world will change massively.

sixQuarks 3y ago

Imagine trying to explain this article to a caveman, or even someone from 200 years ago.

superposeur 3y ago

Do you know if there are any arguments in the literature to the effect that actually useful quantum supremacy may never be possible in principle (not merely in practice)? What I mean is: decoherence with environment must be held at bay long enough for the final answer to appear in the qubits with high probability. Based on examples from thermodynamics (such as impossibility of extracting useful work from a heat reservoir without a second, lower-temperature reservoir into which to dump heat), I could imagine a scenario where decoherence would always foil the computation at some point, perhaps at some intermediate time or in the final measurement. In particular examples, this would show up as irksome experimental limitations, but in fact these limitations would all stem from a deeper prohibition. And to the extent that decoherence could be managed (such as in the cited experiment), the resulting computation would not be "useful".

dekhn 3y ago

the best thing about watching the entire quantum computing debacle is every time somebody says their QC does something faster than a classical computer, somebody tunes the classical computer to beat the QC. Combined with the fact that chip infrastructure is already paid for and there is a large market to enable economy of scale, coupled with the lack of true problems where exponentially better problem solving is critical to business or military success, means we're going to see a series of QC claims that really just prop up classical computers for some time. (I used to work in supercomputing and chemistry and await the day we have useful QCs doing simulation better than what we can do on supercomputers)

pclmulqdq 3y ago
With all of the sensationalization, I am now convinced that many of the people in quantum computing itself are grifters, and that funding agencies keep paying them to put pressure on classical computing (despite knowing that QC is a big grift). Already, optimization problems have seen classical "ising" chips get great results (as good as the quantum annealing chips), proving that optimization doesn't actually need tunneling or superposition. Now, the number theorists just need to come up with a classical analog for a QFT or another similar transform, and we will see them obviate QC here. Arguably, RSA being obsolete has already done this. In simulation, supercomputers are also making huge advances in power.
- bawolff 3y ago
  When people are hyping something that is probably still 20 years out, i think its safe to say they are trying to sell you something. Quantum computers will be a real (albeit not earth shattering) advance, but we are still far off. Still rather people pump money here than crypto bs.
  - pclmulqdq 3y ago
    Quantum computing has been 10 years away for the last 30 years.

moonshadow565 3y ago

How exactly does this make their search engine better?

cbsmith 3y ago
You forget that their real business is ads.

m3kw9 3y ago

So this is similar to the FizzBuzz post where they are trying to make an algorithm to make it the fastest, but really is useless.

neonate 3y ago

https://archive.md/T6viH https://archive.md/T6viH

jscipione 3y ago

Quantum computers make it practical for us to solve problems at much faster speeds, but at what cost? Quantum computers change the quantum state of particles in parallel universes, and likewise quantum computers in other universes change the quantum state of particles in our Universe. What is the effect of this? We should expect to see random otherwise unexplainable changes, and that’s exactly what we’ve seen over the last 10 years, it’s called the “Mandela Effect.” But despite the name referring to an important historic figure most “mandela effects” are tiny almost insignificant changes such as the spelling of The Bernstein Bears or the presence of a Cornucopia in Fruit of the Loom logo, the kind of thing that quantum changes could alter. I realize this is probably too far out there for most Hacker News readers and I’ll get down-voted for it, but I believe there may be a real danger here, and it’s something we need to watch out for as we develop quantum computers further. If we don’t take the threat seriously the Universe we live in now may become different from the one we remember, and we will need to provide safe-guards to retain the consistency of our Universe.