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The article suffers from skipping between layers of abstraction in an attempt to make a point, and in the end in doing so fails to make the initial point. In t

The article suffers from skipping between layers of abstraction in an attempt to make a point, and in the end in doing so fails to make the initial point. In the first "Myth" section, that "nobody understands this quantum stuff", the example is used of the transistor. It's true that we have no way of making a classical model of a transistor, and our understanding of how transistors work relies on quantum mechanics. But we did not invent transistors from quantum physics -- we created transistors long before we had an explanation of how they worked, and we have continued to improve and iterate by making advances in material sciences and experimentation, not by applying first principles. Things like blue LEDs were invented by tinkering rather than by solving Lagrangians. The final section was of particular interest to me; Gil Kalai's work on quantum error correction is very interesting to me and I am in the camp that believes that quantum computing is not possible in any useful sense; in particular a quantum computer will not be capable of being significantly more powerful than a classical computer, in the quantum supremacy sense. Here the author reverts to a simplistic argument that "of course" quantum computers are possible, because we can model a quantum computer in a traditional computer. But this sidesteps the main claims, which are whether it is possible to scale error correction to the point where a useful result can be achieved. Even in the domain of NISQ, which is roughly the equivalent of running fluid dynamics simulation in a bathtub, we have yet to produce results showing that we can scale significantly better than a quantum computer.

neolefty 2y ago
> The final section was of particular interest to me; Gil Kalai's work on quantum error correction is very interesting to me and I am in the camp that believes that quantum computing is not possible in any useful sense; in particular a quantum computer will not be capable of being significantly more powerful than a classical computer, in the quantum supremacy sense. My question too. I've had a vague feeling about this for a long time, waving my hands about thermodynamics with "It must get exponentially harder per qbit to eliminate thermal noise by cooling down closer to absolute zero," and I'd really like to get past my hand-waving and see what the dynamics really are.
- sebzim4500 2y ago
  >It must get exponentially harder per qbit to eliminate thermal noise by cooling down closer to absolute zero Why? Cooling a large object is not exponentially harder than cooling a small object.
  - nyrikki 2y ago
    Surface area is squared, volume is cubed, a larger object has to get hotter to expell the same amount of heat. Per unit of volume, your body produces more heat than the sun, exactly because it is an exponential function.
    - drdeca 2y ago
      Huh? What are you saying is an exponential function? x^3 is not an exponential function, in the sense relevant here.
      - dekhn 2y ago
        What is the right term for "the ratio scales as a power, rather than linearly"?
        sebzim4500 2y ago
        (super-linear) polynomial
        aeonik 2y ago
        For GP: You can be more specific too with quadratic, cubic, etc...
      - nyrikki 2y ago
        You aren't thinking about the exponential decay of emissivity near absolute zero. It isn't linear like we get to assume to make the math easier. Thus why IBMs largest refrigerator can only dissipate tiny amounts when cold. > enabling close to ~10 mW at 100 mK cooling power, and over 24 W of cooling power at 4 K temperatures. Finally, the weight of the entire system — 6.7 metric tons They aren't building single huge quantum processors, but networks of easy to cool parts. IBM hopes that one GoldenEye refrigerator may be able to hold a million qbits but that isn't enough to break RSA. RAND estimated 890 MWh per key to be broken. It will be horizontal sprawl, not vertical integration. Larger objects simply have to get hotter to expell the same watts per volume or increase surface area. That is problematic for quantum computers.
deleted 2y ago
[deleted]
glitchc 2y ago
Relevant reading: https://computerhistory.org/blog/why-analog-computers/ https://computerhistory.org/blog/why-analog-computers/ tl;dr Experts in a domain are extremely poor at predicting the impact of a technology disruptive to their domain. It's not that they are trying to be dishonest. Just that there are too many fallacies waiting to trap them and they inevitably fall prey to one or more of them.
sebzim4500 2y ago
>The final section was of particular interest to me; Gil Kalai's work on quantum error correction is very interesting to me and I am in the camp that believes that quantum computing is not possible in any useful sense; in particular a quantum computer will not be capable of being significantly more powerful than a classical computer, in the quantum supremacy sense. Maybe his arguments have improved over the decades. Does he now have a coherent argument that doesn't (i) take it as a point of religious faith that noise will be magically correlated in order to break error correcting codes (ii) also demonstrate the impossibility of classical computers
- naasking 2y ago
  > (i) take it as a point of religious faith that noise will be magically correlated in order to break error correcting codes This possibility doesn't strike me as any more magical than QM's conjugate variables or its unusual correlations, which also seemed magical to classical physics. Arguably these + contextuality would make noise correlated with the system's configuration in some way, we just don't have a thorough enough understanding of measurement and decoherence to quantify it precisely. I think that's beginning to change, and that we'll have more clarity in the next 10 years or so.
  - sebzim4500 2y ago
    But the reason people believe QM is because of overwhelming empirical evidence, not because it seems right. You can't just go "QM has many surprising aspects" to "this other theory also has surprising aspects, it's probably true". If we had been having this conversation before some of the more bizarre quantum effects had been observed it would have been a fair comparison, but we are way past that point.
    - naasking 2y ago
      > You can't just go "QM has many surprising aspects" to "this other theory also has surprising aspects, it's probably true". I didn't say it's probably true because of this argument, you're saying it's probably false because it seems magical, and that's the implication I'm disputing with that analogy. I do think it's plausible that noise could be correlated for the reasons I specified, but not because of the "magical" analogy.
JanisErdmanis 2y ago
> But we did not invent transistors from quantum physics -- we created transistors long before we had an explanation of how they worked, and we have continued to improve and iterate by making advances in material sciences and experimentation, not by applying first principles. Things like blue LEDs were invented by tinkering rather than by solving Lagrangians. In a similar spirit ships were built, steam engines made and applications of superconductivity imagined long before the objects were understood from first principles. Creation often proceeded theory nevertheless it is still useful for optimizing designs at later stages.
NickC25 2y ago
>I am in the camp that believes that quantum computing is not possible in any useful sense; in particular a quantum computer will not be capable of being significantly more powerful than a classical computer, in the quantum supremacy sense. Could you elaborate on that? I was under the impression that some companies are using Quantum Computers because quantum supremacy has been demonstrated (such as in molecular modeling for drug discovery or materials science) - but I'm a complete novice here, and would love to learn more. I'm probably quite wrong, and happy to be corrected. Also, by not possible in a useful sense, do you mean that QCs as they are now versus in N years, or just in general?
- dumbo-octopus 2y ago
  There are no quantum computers in practical use at the moment. This essay^ by IBM (incredibly biased towards making quantum computing seem useful) provides many "visions of"'s and "potential to"'s and "may benefit"'s, but nothing in the present tense. ^https://www.ibm.com/quantum/blog/quantum-working-groups https://www.ibm.com/quantum/blog/quantum-working-groups
- andrewla 2y ago
  When I say that quantum computing is not possible, I mean in general. It's a dead end. Note that this belief is subject to being falsified by progress in the field or a demonstration of error correction at scale. There are companies selling and companies using "Quantum Computers". For example, D-Wave systems sells a computer that uses quantum annealing so solve a class of minimization problems. To date, there is no quantum computer, in a commercial or a research setting, that has demonstrated it can compute anything faster than a classical computer (this includes the D-Wave systems). The current trend is to try to establish quantum supremacy (and thus falsify the error correction is impossible thesis) through building extremely simple (non-general purpose) quantum systems. Most recently Google announced a successful attempt that has since been invalidated.

neolefty 2y ago

> The final section was of particular interest to me; Gil Kalai's work on quantum error correction is very interesting to me and I am in the camp that believes that quantum computing is not possible in any useful sense; in particular a quantum computer will not be capable of being significantly more powerful than a classical computer, in the quantum supremacy sense. My question too. I've had a vague feeling about this for a long time, waving my hands about thermodynamics with "It must get exponentially harder per qbit to eliminate thermal noise by cooling down closer to absolute zero," and I'd really like to get past my hand-waving and see what the dynamics really are.

sebzim4500 2y ago
>It must get exponentially harder per qbit to eliminate thermal noise by cooling down closer to absolute zero Why? Cooling a large object is not exponentially harder than cooling a small object.
- nyrikki 2y ago
  Surface area is squared, volume is cubed, a larger object has to get hotter to expell the same amount of heat. Per unit of volume, your body produces more heat than the sun, exactly because it is an exponential function.
  - drdeca 2y ago
    Huh? What are you saying is an exponential function? x^3 is not an exponential function, in the sense relevant here.
    - dekhn 2y ago
      What is the right term for "the ratio scales as a power, rather than linearly"?
      - sebzim4500 2y ago
        (super-linear) polynomial
        aeonik 2y ago
        For GP: You can be more specific too with quadratic, cubic, etc...
    - nyrikki 2y ago
      You aren't thinking about the exponential decay of emissivity near absolute zero. It isn't linear like we get to assume to make the math easier. Thus why IBMs largest refrigerator can only dissipate tiny amounts when cold. > enabling close to ~10 mW at 100 mK cooling power, and over 24 W of cooling power at 4 K temperatures. Finally, the weight of the entire system — 6.7 metric tons They aren't building single huge quantum processors, but networks of easy to cool parts. IBM hopes that one GoldenEye refrigerator may be able to hold a million qbits but that isn't enough to break RSA. RAND estimated 890 MWh per key to be broken. It will be horizontal sprawl, not vertical integration. Larger objects simply have to get hotter to expell the same watts per volume or increase surface area. That is problematic for quantum computers.

deleted 2y ago

[deleted]

glitchc 2y ago

Relevant reading: https://computerhistory.org/blog/why-analog-computers/ https://computerhistory.org/blog/why-analog-computers/ tl;dr Experts in a domain are extremely poor at predicting the impact of a technology disruptive to their domain. It's not that they are trying to be dishonest. Just that there are too many fallacies waiting to trap them and they inevitably fall prey to one or more of them.

sebzim4500 2y ago

>The final section was of particular interest to me; Gil Kalai's work on quantum error correction is very interesting to me and I am in the camp that believes that quantum computing is not possible in any useful sense; in particular a quantum computer will not be capable of being significantly more powerful than a classical computer, in the quantum supremacy sense. Maybe his arguments have improved over the decades. Does he now have a coherent argument that doesn't (i) take it as a point of religious faith that noise will be magically correlated in order to break error correcting codes (ii) also demonstrate the impossibility of classical computers

naasking 2y ago
> (i) take it as a point of religious faith that noise will be magically correlated in order to break error correcting codes This possibility doesn't strike me as any more magical than QM's conjugate variables or its unusual correlations, which also seemed magical to classical physics. Arguably these + contextuality would make noise correlated with the system's configuration in some way, we just don't have a thorough enough understanding of measurement and decoherence to quantify it precisely. I think that's beginning to change, and that we'll have more clarity in the next 10 years or so.
- sebzim4500 2y ago
  But the reason people believe QM is because of overwhelming empirical evidence, not because it seems right. You can't just go "QM has many surprising aspects" to "this other theory also has surprising aspects, it's probably true". If we had been having this conversation before some of the more bizarre quantum effects had been observed it would have been a fair comparison, but we are way past that point.
  - naasking 2y ago
    > You can't just go "QM has many surprising aspects" to "this other theory also has surprising aspects, it's probably true". I didn't say it's probably true because of this argument, you're saying it's probably false because it seems magical, and that's the implication I'm disputing with that analogy. I do think it's plausible that noise could be correlated for the reasons I specified, but not because of the "magical" analogy.

JanisErdmanis 2y ago

> But we did not invent transistors from quantum physics -- we created transistors long before we had an explanation of how they worked, and we have continued to improve and iterate by making advances in material sciences and experimentation, not by applying first principles. Things like blue LEDs were invented by tinkering rather than by solving Lagrangians. In a similar spirit ships were built, steam engines made and applications of superconductivity imagined long before the objects were understood from first principles. Creation often proceeded theory nevertheless it is still useful for optimizing designs at later stages.

NickC25 2y ago

>I am in the camp that believes that quantum computing is not possible in any useful sense; in particular a quantum computer will not be capable of being significantly more powerful than a classical computer, in the quantum supremacy sense. Could you elaborate on that? I was under the impression that some companies are using Quantum Computers because quantum supremacy has been demonstrated (such as in molecular modeling for drug discovery or materials science) - but I'm a complete novice here, and would love to learn more. I'm probably quite wrong, and happy to be corrected. Also, by not possible in a useful sense, do you mean that QCs as they are now versus in N years, or just in general?

dumbo-octopus 2y ago
There are no quantum computers in practical use at the moment. This essay^ by IBM (incredibly biased towards making quantum computing seem useful) provides many "visions of"'s and "potential to"'s and "may benefit"'s, but nothing in the present tense. ^https://www.ibm.com/quantum/blog/quantum-working-groups https://www.ibm.com/quantum/blog/quantum-working-groups
andrewla 2y ago
When I say that quantum computing is not possible, I mean in general. It's a dead end. Note that this belief is subject to being falsified by progress in the field or a demonstration of error correction at scale. There are companies selling and companies using "Quantum Computers". For example, D-Wave systems sells a computer that uses quantum annealing so solve a class of minimization problems. To date, there is no quantum computer, in a commercial or a research setting, that has demonstrated it can compute anything faster than a classical computer (this includes the D-Wave systems). The current trend is to try to establish quantum supremacy (and thus falsify the error correction is impossible thesis) through building extremely simple (non-general purpose) quantum systems. Most recently Google announced a successful attempt that has since been invalidated.