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When a quantum computer is put to work on a problem, it considers all possible answers by simultaneously arranging its qubits into every combination of "zeroes"

by rw 17y ago

When a quantum computer is put to work on a problem, it considers all possible answers by simultaneously arranging its qubits into every combination of "zeroes" and "ones." This has got to stop.

PieSquared 17y ago
I've heard this dozens of times, and I know every time that it's crazy. But I haven't really managed to figure out what part of this 'rumor' is actually true. Do you mind explaining where this idea comes from, and whether it's remotely right, or what?
- scythe 17y ago
  This should clear things up: http://en.wikipedia.org/wiki/Qubit http://en.wikipedia.org/wiki/Qubit Also this: http://www.het.brown.edu/people/andre/qlambda/index.html http://www.het.brown.edu/people/andre/qlambda/index.html but the basic idea is that quantum computers allow operations to be taken on an entire list simultaneously (entanglement).
  - joe_the_user 17y ago
    So does hacker news have a problem with quantum mechanics being explainable? ?
    - gjm11 17y ago
      No. With quantum mechanics being explained wrong.
joe_the_user 17y ago
What do you mean? Quantum mechanics is indeed a different viewpoint As I recall, the Feynman diagram approach assumes that every conceivable interaction between particles that could happen does happen with a given probability depending on the interaction's complexity. Indeed, the Heisenberg Uncertainty Principle is quite a mind fuck - if you know the exact speed of a particle, the location of particle become utterly uncertain to the point that it could be anywhere in the universe. So what specifically is your problem with the above quote?
- Confusion 17y ago
  What is wrong is that a quantum computer doesn't consider all possible answers at the same time. Although the qubits are in a 'combination' of two possible final states. it's not as if each state represents one of the answers to the question. During a computation on your current computer the bits involved in the computation don't evolve towards an answer either (although a subset of them will).
- rw 17y ago
  Your comment is painfully embarrassing to read. Instead of attacking what I said (or me), try asking: "could you elaborate on what you think the article is misrepresenting?".
jackfoxy 17y ago
"This has got to stop." Popular science journalists always fall back on the simplified multi-universe explanation to explain quantum computing. I wish they would adopt another paradigm too, but in general I want to see a better quality of synopses of technical papers in popular journalism. Getting back to the subject of the article... Scott Aaronson has always said the most interesting use of quantum computing would be to simulate natural processes. This may be the first significant achievement of that. (At least that I have heard of.)
- joe_the_user 17y ago
  The many-worlds interpretation of quantum mechanics is a consistent viewpoint that fits with the standard equations of Quantum Mechanics: http://en.wikipedia.org/wiki/Many-worlds_interpretation http://en.wikipedia.org/wiki/Many-worlds_interpretation If it also happens to correspond to human intuition, I'm not sure exactly what the problem is.
  - jackfoxy 17y ago
    I'm objecting to the dumbed-down version of the many worlds interpretation as an explaination of quantum computing because it gives the impression quantum computing can do things it can't actually do, like solve NP-complete problems efficiently, which is not currently theorized, let alone proven.
    - deleted 17y ago
      [deleted]
      - rw 17y ago
        "a task which is believed to be NP-hard" CITATION NEEDED
michael_nielsen 17y ago
I doubt it will ever stop. It's too appealing for journalists, and a lot easier than explaining the true state of affairs. I have story about this which I can't resist telling. It really annoyed me at the time, but with a few years distance I think it's both funny and illustrative of media stories about quantum computing. In 2001, I was interviewed about quantum computing by a reporter (from the Sydney Morning Herald, if I recall correctly) who repeatedly asked me for a "simple, concrete explanation" of how quantum computers work. If you take this request really (really!) literally, such an explanation probably isn't possible. If it was, you could efficiently simulate the elements of the explanation on a conventional computer, and quantum computers would offer no real advantage over conventional computers. In fact, in my opinion, what's interesting about quantum computing is precisely the gap between our ability to give such a simple, concrete explanation and what's really going on. You _can_ give a (fairly) simple indirect explanation of how they work - simple if someone's comfortable with complex numbers and vectors - but it is pretty indirect. I explained this to the reporter, who made all the right noises, and then gave him the "simultaneously in all possible states" explanation as an example of the kind of nonsense that sounds good, but actually obscures the truth of what's going on. You can probably guess the rest: when the article came out, I was in there, quoted saying something along the lines of "When a quantum computer is put to work on a problem, it considers all possible answer by simultaneously arranging..." The problem is that this line is just too tempting and pat a story for reporters. It creates the illusion of understanding (in my opinion), while leaving the more complex truth undisturbed.

by rw 17y ago

When a quantum computer is put to work on a problem, it considers all possible answers by simultaneously arranging its qubits into every combination of "zeroes" and "ones." This has got to stop.

PieSquared 17y ago

I've heard this dozens of times, and I know every time that it's crazy. But I haven't really managed to figure out what part of this 'rumor' is actually true. Do you mind explaining where this idea comes from, and whether it's remotely right, or what?

scythe 17y ago
This should clear things up: http://en.wikipedia.org/wiki/Qubit http://en.wikipedia.org/wiki/Qubit Also this: http://www.het.brown.edu/people/andre/qlambda/index.html http://www.het.brown.edu/people/andre/qlambda/index.html but the basic idea is that quantum computers allow operations to be taken on an entire list simultaneously (entanglement).
- joe_the_user 17y ago
  So does hacker news have a problem with quantum mechanics being explainable? ?
  - gjm11 17y ago
    No. With quantum mechanics being explained wrong.

joe_the_user 17y ago

What do you mean? Quantum mechanics is indeed a different viewpoint As I recall, the Feynman diagram approach assumes that every conceivable interaction between particles that could happen does happen with a given probability depending on the interaction's complexity. Indeed, the Heisenberg Uncertainty Principle is quite a mind fuck - if you know the exact speed of a particle, the location of particle become utterly uncertain to the point that it could be anywhere in the universe. So what specifically is your problem with the above quote?

Confusion 17y ago
What is wrong is that a quantum computer doesn't consider all possible answers at the same time. Although the qubits are in a 'combination' of two possible final states. it's not as if each state represents one of the answers to the question. During a computation on your current computer the bits involved in the computation don't evolve towards an answer either (although a subset of them will).
rw 17y ago
Your comment is painfully embarrassing to read. Instead of attacking what I said (or me), try asking: "could you elaborate on what you think the article is misrepresenting?".

jackfoxy 17y ago

"This has got to stop." Popular science journalists always fall back on the simplified multi-universe explanation to explain quantum computing. I wish they would adopt another paradigm too, but in general I want to see a better quality of synopses of technical papers in popular journalism. Getting back to the subject of the article... Scott Aaronson has always said the most interesting use of quantum computing would be to simulate natural processes. This may be the first significant achievement of that. (At least that I have heard of.)

joe_the_user 17y ago
The many-worlds interpretation of quantum mechanics is a consistent viewpoint that fits with the standard equations of Quantum Mechanics: http://en.wikipedia.org/wiki/Many-worlds_interpretation http://en.wikipedia.org/wiki/Many-worlds_interpretation If it also happens to correspond to human intuition, I'm not sure exactly what the problem is.
- jackfoxy 17y ago
  I'm objecting to the dumbed-down version of the many worlds interpretation as an explaination of quantum computing because it gives the impression quantum computing can do things it can't actually do, like solve NP-complete problems efficiently, which is not currently theorized, let alone proven.
  - deleted 17y ago
    [deleted]
    - rw 17y ago
      "a task which is believed to be NP-hard" CITATION NEEDED

michael_nielsen 17y ago

I doubt it will ever stop. It's too appealing for journalists, and a lot easier than explaining the true state of affairs. I have story about this which I can't resist telling. It really annoyed me at the time, but with a few years distance I think it's both funny and illustrative of media stories about quantum computing. In 2001, I was interviewed about quantum computing by a reporter (from the Sydney Morning Herald, if I recall correctly) who repeatedly asked me for a "simple, concrete explanation" of how quantum computers work. If you take this request really (really!) literally, such an explanation probably isn't possible. If it was, you could efficiently simulate the elements of the explanation on a conventional computer, and quantum computers would offer no real advantage over conventional computers. In fact, in my opinion, what's interesting about quantum computing is precisely the gap between our ability to give such a simple, concrete explanation and what's really going on. You _can_ give a (fairly) simple indirect explanation of how they work - simple if someone's comfortable with complex numbers and vectors - but it is pretty indirect. I explained this to the reporter, who made all the right noises, and then gave him the "simultaneously in all possible states" explanation as an example of the kind of nonsense that sounds good, but actually obscures the truth of what's going on. You can probably guess the rest: when the article came out, I was in there, quoted saying something along the lines of "When a quantum computer is put to work on a problem, it considers all possible answer by simultaneously arranging..." The problem is that this line is just too tempting and pat a story for reporters. It creates the illusion of understanding (in my opinion), while leaving the more complex truth undisturbed.