Slashdot Mirror

← Back to Stories (view on slashdot.org)

Is Quantum Computing Impossible? (ieee.org)

Posted by EditorDavid on from the qubits-and-bytes dept.

"Quantum computing is complex and it's not all it's cracked up to be," writes Slashdot reader nickwinlund77, pointing to this new article from IEEE Spectrum arguing it's "not in our foreseeable future": Having spent decades conducting research in quantum and condensed-matter physics, I've developed my very pessimistic view. It's based on an understanding of the gargantuan technical challenges that would have to be overcome to ever make quantum computing work.... Experts estimate that the number of qubits needed for a useful quantum computer, one that could compete with your laptop in solving certain kinds of interesting problems, is between 1,000 and 100,000. So the number of continuous parameters describing the state of such a useful quantum computer at any given moment must be at least 2**1,000, which is to say about 10**300. That's a very big number indeed. How big? It is much, much greater than the number of subatomic particles in the observable universe. To repeat: A useful quantum computer needs to process a set of continuous parameters that is larger than the number of subatomic particles in the observable universe. At this point in a description of a possible future technology, a hardheaded engineer loses interest....

[I]t's absolutely unimaginable how to keep errors under control for the 10300 continuous parameters that must be processed by a useful quantum computer. Yet quantum-computing theorists have succeeded in convincing the general public that this is feasible.... Even without considering these impossibly large numbers, it's sobering that no one has yet figured out how to combine many physical qubits into a smaller number of logical qubits that can compute something useful. And it's not like this hasn't long been a key goal.... On the hardware front, advanced research is under way, with a 49-qubit chip (Intel), a 50-qubit chip (IBM), and a 72-qubit chip (Google) having recently been fabricated and studied. The eventual outcome of this activity is not entirely clear, especially because these companies have not revealed the details of their work...

I believe that, appearances to the contrary, the quantum computing fervor is nearing its end. That's because a few decades is the maximum lifetime of any big bubble in technology or science. After a certain period, too many unfulfilled promises have been made, and anyone who has been following the topic starts to get annoyed by further announcements of impending breakthroughs. What's more, by that time all the tenured faculty positions in the field are already occupied. The proponents have grown older and less zealous, while the younger generation seeks something completely new and more likely to succeed.
He advises quantum computing researchers to follow the advice of IBM physicist Rolf Landauer. Decades ago Landauer warned quantum computing's proponents that they needed a disclaimer in all of their publications.

"This scheme, like all other schemes for quantum computation, relies on speculative technology, does not in its current form take into account all possible sources of noise, unreliability and manufacturing error, and probably will not work."

7 of 222 comments (clear)

  1. Huh? by JaredOfEuropa · · Score: 4, Insightful

    A useful quantum computer needs to process a set of continuous parameters that is larger than the number of subatomic particles in the observable universe

    I thought that the whole point of quantum computers was that there's no need to describe or process all possible states. And that the difficulty of practical quantum computers is that the qubits need to "work together": you can't just make 1 cubit, then make 1023 more and build yourself a 1024 cubit computer.

    The guy obviously knows way more about quantum computers than I do. But I've never seen the difficulties of quantum computing described in this manner.

    --
    If construction was anything like programming, an incorrectly fitted lock would bring down the entire building...
    1. Re:Huh? by Ramze · · Score: 3, Insightful

      I tend to agree, and apparently so do IBM, Google, et al. Still, the larger the system, the more error prone it becomes. Obviously, we have quantum computers (or at least functioning parts of ones) working today and can entangle up to 50 qubits or more with relative stability... but, the question is whether we can do it at the scale needed to be "useful" (according to this individual) without losing the signal for all the noise.

      This person's perspective is that what we naively see as an engineering problem to be resolved with future refinements is actually an issue that can't be resolved because nature at a fundamental particle physics level can't be controlled or tuned to the degree necessary to get one working, nor reasonably checked for accuracy because the states to be checked are beyond astronomical.

    2. Re:Huh? by sjames · · Score: 3, Insightful

      Hot fusion is also "just an engineering problem".

    3. Re:Huh? by Anonymous Coward · · Score: 2, Insightful

      Hot fusion is also "just an engineering problem".

      Using the word "also" makes it look like you are grouping fusion and quantum computing into the same level of possible, which is both not true and possibly showing a deep misunderstanding of the phrase "just an engineering problem"

      It comes down to how different people use the word "impossible"

      To some, impossible means the laws of physics explicitly do not allow it.
      To others, impossible means the laws of physics may not yet exclude it but there are no examples to demonstrate it could happen.

      "Just an engineering problem" was coined specifically for people who use the word "impossible" to describe something that is currently happening on a massive scale and clearly possible, but human beings can't do it.

      Yes, fusion is "just an engineering problem" because it is happening, with every star including our sun, and has been occurring for billions of years.
      That fact alone demonstrates that it is in fact possible. It is happening. Claims it is impossible to occur are just outright false.

      Quantum computing however isn't the same thing. There are no examples of it happening to point to and prove its possibility. All we have is that the laws of physics don't seem to exclude it as an option.
      That is NOT what "just an engineering problem" applies to.

      "Engineering" is taking a process and making it happen.
      That process needs to be defined first, and if it isn't, means there is *nothing* an engineer can do about it.

      From a physics perspective, fusion is pretty simple. Apply enough pressure and force to atoms so their electron shells overlap.
      From an engineering perspective, that may be straight forward but is FAR from simple to accomplish.

      Quantum computing on the other hand is not simple. We have nothing in nature doing that to follow. We have guesses and assumptions many of which haven't been shown as fact. There is damn little to engineer about it all.

      The phrase pretty much only applies when people claim as impossible things that are already occurring and clearly possible.
      Anything not demonstrated as possible isn't in the realm of engineering because it very well may not be possible until that proof is shown.

  2. Not impossible... just even harder to exploit by igor.sfiligoi · · Score: 5, Insightful

    The author makes a great point about the near impossibility of perfect, error-free quantum computation.
    But this has been realized a few years back by most quantum algorithm developers, too.

    Many recent algorithms assume that the quantum computation will be partially faulty.
    And they work around it.

    Yes, that makes these algorithms harder to design and they are less efficient compared to the ones assuming no errors, but they still seem to provide a way forward.
    I would definitely not write off quantum computing yet.

  3. Makes no sense by cryptizard · · Score: 4, Insightful

    So the number of continuous parameters describing the state of such a useful quantum computer at any given moment must be at least 2**1,000, which is to say about 10**300. That's a very big number indeed. How big? It is much, much greater than the number of subatomic particles in the observable universe.

    I am struggling to come up with some way that this part makes any sense at all. It sounds like the kind of thing someone who is definitely not an expert the area would say. He is expressing the number of possible configurations of 1,000 qubits but that is only something you care about if you are simulating a quantum computer with a classical one. The whole point of quantum computers is that you don't have to do that.

    Also a simple counterexample to this sentiment is given later on, when mentioning that Google already has a 72-qubit computer. Just storing the states of a 72-qubit machine would be substantially more than the entire capacity of the internet, implying that since we somehow did it then enumerating all the states is not necessary.

  4. Re:Simple answer by glenebob · · Score: 3, Insightful

    Yep. You can use it crack certain cryptography problems faster; problem though, the algorithm scales differently and doubling the key size makes it much harder to crack. Whereas, using traditional brute force on regular computers, doubling the key size only helps a little bit.

    Is it opposite day? I must have missed the tweet.