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How sure are we that quantum computing will ever work? I think this boils down to whether the wave function collapses as expected(?) Perhaps reality is actuall

by m101 5y ago

How sure are we that quantum computing will ever work? I think this boils down to whether the wave function collapses as expected(?) Perhaps reality is actually only approximated by the wave function but reality is something else under the surface which means quantum computers may need to be reconsidered.

gameswithgo 5y ago
The only barriers to them working are engineering challenges which may prove insurmountable, may not. There are not any theoretical considerations that would make them not work.
- ericpauley 5y ago
  There are certainly possible reasons why quantum computing could be impossible. To me the most compelling of these would be that the error rate of physical qubits might fundamentally always exceed the threshold for correction with any real ECC as the number of logical qubits increases. I highly recommend reading [1] for an overview of the various skeptical viewpoints on quantum computing. Note that, while Aaronson argues most of the initial arguments are trivially wrong, he admits that whether or not error correction is fundamentally impossible is an open question. [1] https://www.scottaaronson.com/democritus/lec14.html https://www.scottaaronson.com/democritus/lec14.html
  - Jensson 5y ago
    Trying to build a quantum computer is probably a good way to learn more about quantum interactions, since it would stress those to its limits to work.
- Azsy 5y ago
  I've always seen it the other way around. We can keep solving the engineering challenges, but the universe might simply not allow us to get a return on investment with every additional qubit.
- stephc_int13 5y ago
  We can also consider Alcubierre drive to be an engineering problem, don't you think?
  - tsimionescu 5y ago
    Not really, the Alcubierre drive depends on things we have no reason to think exist in the universe (negative energy). It's also likely that the Alcubierre drive doesn't actually allow accelerating from slower than light speeds to higher than light speeds. QC in contrast must exist or else QM is fundamentally wrong - not incomplete, but wrong.
andi999 5y ago
How sure are we with fusion reactors? Probably both 50/50.
- Azsy 5y ago
  They are not similar at all. We know its possible to have a fusion reactor, we would just have to dump enough mass together to build a sun. Hopefully we can make it more cost effective. There isn't a natural phenomena that solves a problem by encoding it and (ab)using quantum physics.
  - jl2718 5y ago
    Have you heard of Riemannium? (not serious) https://arxiv.org/abs/nlin/0101014 https://arxiv.org/abs/nlin/0101014
gaze 5y ago
1. We aren't 2. Everything after the first sentence doesn't make sense. Any system that implements a restricted class of unitaries and features local measurement as described by Born's rule can efficiently solve problems in BQP. We have no reason this should apply to 10 qubits and not 1000. The theory of quantum mechanics has been completely predictive in materials and has resulted in the most accurate predictions in nature (Anomalous magnetic dipole moment to a part in a trillion.) It doesn't matter if the theory is "Macroscopic" or whatever, it's predictive and within the constraints of its predictions you have known computational power up to problems in BQP. Whether BQP=P is an open question, but as is P=NP. Known problems are things like wiring, materials science/sources of noise -- eventually including things like cosmic rays. It should work and we have no reason to think it shouldn't due to fundamental limitations of the natural world. It is, however, one of the hardest scientific things humans have ever tried to do so far. To say it'll definitely work is hubristic.
- lisper 5y ago
  This is not quite true. There are spontaneous collapse models [1] that are consistent with the data, like the GRW model [2]. Personally I give long odds against these being true, but you can't rule them out on the basis of current data. And if they are true then they would present a fundamental limit on how big you can make a quantum computer before it fails. [1] https://plato.stanford.edu/entries/qm-collapse/#ContSponLocaModeCSL https://plato.stanford.edu/entries/qm-collapse/#ContSponLoca... [2] https://en.wikipedia.org/wiki/Ghirardi%E2%80%93Rimini%E2%80%93Weber_theory https://en.wikipedia.org/wiki/Ghirardi%E2%80%93Rimini%E2%80%...
  - gaze 5y ago
    There have been superpositions maintained on the scale of a meter using these fountain experiments. I think the chip traps, SC qubit chips, dot chips, etc… will be much smaller than this.
    - lisper 5y ago
      Not sure what you're referring to here. Maintaining a superposition is not hard. The light from distant galaxies has been in superposition across literally billions of (light) years before we detect it. What is harder to maintain over large distances are entanglements, but even those have been maintained across hundreds of miles. When I talked about a "fundamental limit on how big you can make a quantum computer" I wasn't talking about it's physical size, I was talking about the number of mutually entangled qbits it contains, and the amount of time it is able to maintain those entanglements in a coherent state.
Strilanc 5y ago
This is part of the reason I like that the first phase of Google's current quantum computer roadmap is "physics derisking" [1]. There's no known reason that it should be impossible to make a thousand qubits dance together in a highly controlled way and get the expected results, but maybe there are some unexpected or unknown obstacles. That being said, if physics derisking failed, it seems really unlikely to me that it would be because quantum mechanics itself was wrong as opposed to there just being some unforseen problematic error mechanism that was consistent with quantum mechanics. Finding a flaw in quantum mechanics itself would be a scientific revolution, which would be awesome, but those are also pretty rare. I also think it's a little telling that people keep thinking it's the philosophically unsatisfying parts of quantum mechanics that are going to break, when entering a new regime. It smells of confirmation bias. Disclaimer: am on google quantum team. 1: https://youtu.be/VvHh6GoNhy8?t=311 https://youtu.be/VvHh6GoNhy8?t=311
yk 5y ago
> How sure are we that quantum computing will ever work? Up to 12 qubits or so. > Perhaps reality is actually only approximated by the wave function but reality is something else under the surface which means quantum computers may need to be reconsidered. Possible, that reality is only approximated, and that approximation breaks down at more qubits. However, that would be the more exiting outcome, since then we have an experiment that gives us a window into a post quantum theory.

by m101 5y ago

gameswithgo 5y ago

The only barriers to them working are engineering challenges which may prove insurmountable, may not. There are not any theoretical considerations that would make them not work.

ericpauley 5y ago
There are certainly possible reasons why quantum computing could be impossible. To me the most compelling of these would be that the error rate of physical qubits might fundamentally always exceed the threshold for correction with any real ECC as the number of logical qubits increases. I highly recommend reading [1] for an overview of the various skeptical viewpoints on quantum computing. Note that, while Aaronson argues most of the initial arguments are trivially wrong, he admits that whether or not error correction is fundamentally impossible is an open question. [1] https://www.scottaaronson.com/democritus/lec14.html https://www.scottaaronson.com/democritus/lec14.html
- Jensson 5y ago
  Trying to build a quantum computer is probably a good way to learn more about quantum interactions, since it would stress those to its limits to work.
Azsy 5y ago
I've always seen it the other way around. We can keep solving the engineering challenges, but the universe might simply not allow us to get a return on investment with every additional qubit.
stephc_int13 5y ago
We can also consider Alcubierre drive to be an engineering problem, don't you think?
- tsimionescu 5y ago
  Not really, the Alcubierre drive depends on things we have no reason to think exist in the universe (negative energy). It's also likely that the Alcubierre drive doesn't actually allow accelerating from slower than light speeds to higher than light speeds. QC in contrast must exist or else QM is fundamentally wrong - not incomplete, but wrong.

andi999 5y ago

How sure are we with fusion reactors? Probably both 50/50.

Azsy 5y ago
They are not similar at all. We know its possible to have a fusion reactor, we would just have to dump enough mass together to build a sun. Hopefully we can make it more cost effective. There isn't a natural phenomena that solves a problem by encoding it and (ab)using quantum physics.
- jl2718 5y ago
  Have you heard of Riemannium? (not serious) https://arxiv.org/abs/nlin/0101014 https://arxiv.org/abs/nlin/0101014

gaze 5y ago

1. We aren't 2. Everything after the first sentence doesn't make sense. Any system that implements a restricted class of unitaries and features local measurement as described by Born's rule can efficiently solve problems in BQP. We have no reason this should apply to 10 qubits and not 1000. The theory of quantum mechanics has been completely predictive in materials and has resulted in the most accurate predictions in nature (Anomalous magnetic dipole moment to a part in a trillion.) It doesn't matter if the theory is "Macroscopic" or whatever, it's predictive and within the constraints of its predictions you have known computational power up to problems in BQP. Whether BQP=P is an open question, but as is P=NP. Known problems are things like wiring, materials science/sources of noise -- eventually including things like cosmic rays. It should work and we have no reason to think it shouldn't due to fundamental limitations of the natural world. It is, however, one of the hardest scientific things humans have ever tried to do so far. To say it'll definitely work is hubristic.

lisper 5y ago
This is not quite true. There are spontaneous collapse models [1] that are consistent with the data, like the GRW model [2]. Personally I give long odds against these being true, but you can't rule them out on the basis of current data. And if they are true then they would present a fundamental limit on how big you can make a quantum computer before it fails. [1] https://plato.stanford.edu/entries/qm-collapse/#ContSponLocaModeCSL https://plato.stanford.edu/entries/qm-collapse/#ContSponLoca... [2] https://en.wikipedia.org/wiki/Ghirardi%E2%80%93Rimini%E2%80%93Weber_theory https://en.wikipedia.org/wiki/Ghirardi%E2%80%93Rimini%E2%80%...
- gaze 5y ago
  There have been superpositions maintained on the scale of a meter using these fountain experiments. I think the chip traps, SC qubit chips, dot chips, etc… will be much smaller than this.
  - lisper 5y ago
    Not sure what you're referring to here. Maintaining a superposition is not hard. The light from distant galaxies has been in superposition across literally billions of (light) years before we detect it. What is harder to maintain over large distances are entanglements, but even those have been maintained across hundreds of miles. When I talked about a "fundamental limit on how big you can make a quantum computer" I wasn't talking about it's physical size, I was talking about the number of mutually entangled qbits it contains, and the amount of time it is able to maintain those entanglements in a coherent state.

Strilanc 5y ago

This is part of the reason I like that the first phase of Google's current quantum computer roadmap is "physics derisking" [1]. There's no known reason that it should be impossible to make a thousand qubits dance together in a highly controlled way and get the expected results, but maybe there are some unexpected or unknown obstacles. That being said, if physics derisking failed, it seems really unlikely to me that it would be because quantum mechanics itself was wrong as opposed to there just being some unforseen problematic error mechanism that was consistent with quantum mechanics. Finding a flaw in quantum mechanics itself would be a scientific revolution, which would be awesome, but those are also pretty rare. I also think it's a little telling that people keep thinking it's the philosophically unsatisfying parts of quantum mechanics that are going to break, when entering a new regime. It smells of confirmation bias. Disclaimer: am on google quantum team. 1: https://youtu.be/VvHh6GoNhy8?t=311 https://youtu.be/VvHh6GoNhy8?t=311

yk 5y ago

> How sure are we that quantum computing will ever work? Up to 12 qubits or so. > Perhaps reality is actually only approximated by the wave function but reality is something else under the surface which means quantum computers may need to be reconsidered. Possible, that reality is only approximated, and that approximation breaks down at more qubits. However, that would be the more exiting outcome, since then we have an experiment that gives us a window into a post quantum theory.