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> until we figure out why nature keeps blocking us A quantum computer only behaves like our mathematical ideal quantum computer if it's sufficiently isolated f

> until we figure out why nature keeps blocking us A quantum computer only behaves like our mathematical ideal quantum computer if it's sufficiently isolated from the rest of the universe: otherwise you don't get the “indistinguishable states” thing and the amplitudes don't sum, and the computer stops computing and starts being a regular ol' physics experiment. It's an engineering problem, as far as I understand. Get things cold enough, get things isolated enough, so they stay entangled with each other and not with the rest of the universe.

pishpash 5y ago
Is it? In engineering problems you have to consider practical feasibility. Would it turn out that for the expenditure of energy to get things isolated we may as well spend it on classical computation?
- wizzwizz4 5y ago
  On Earth? Maybe. In deep space? Probably not.
  - evanb 5y ago
    The cosmic microwave background makes even deep intergalactic space warmer (3 or 4 K) than the inside of Earth’s best fridges (the best as low as nanoK). 3 or 4 K is easy to achieve using liquid helium cooling, which is presumably why eg. Google’s Sycamore chip operators in that range. But achieving those low temperatures is a regular occurrence in labs all over the world—-you call AirGas or somebody and they deliver a dewar of liquid He.
    - wizzwizz4 5y ago
      And, close to a star, you have several neutrinos flying through your experiment. You have vibrations from earthquakes. You have electromagnetic coupling. etc, etc. The temperatures are easy enough; you just have to compensate for thermal noise. The isolation isn't; without isolation, your signal is wrong.
      - pishpash 5y ago
        But unless you're doing a computation without I/O (i.e. no reading back the results, no providing inputs), you need coupling into the rest of the universe, and typically into a low-entropy part of the universe like the Earth, where you have entities that care about the computation. So, I am not convinced having a deeply isolated part of the universe is the answer; in fact, the isolation vs. signal quality tradeoff makes it sound more and more like a fundamental limitation of practical concern.
        wizzwizz4 5y ago
        > But unless you're doing a computation without I/O (i.e. no reading back the results, no providing inputs), you need coupling into the rest of the universe, and typically into a low-entropy part of the universe like the Earth, where you have entities that care about the computation. With a quantum computer, you can only do that at the end of the computation. Not half-way through; that'll cause the computer to start doing a different (unwanted) computation instead. While the calculation is happening, you need (a high probability of) total isolation from the rest of the universe, so that the intermediate state of the computer only interferes with itself. > So, I am not convinced having a deeply isolated part of the universe is the answer; in fact, the isolation vs. signal quality tradeoff makes it sound more and more like a fundamental limitation of practical concern. It is a fundamental limitation of practical concern! Just like the need to keep conventional computer processors cool or they melt, or the fundamental limitations on the bandwidth that a radio frequency can give you. The people who deal with these limitations are called engineers.
- deleted 5y ago
  [deleted]
octoberfranklin 5y ago
> It's an engineering problem, as far as I understand. That is far from being clear. People in the 1700s were totally convinced that building a perpetual motion machine was just "an engineering problem".

pishpash 5y ago

Is it? In engineering problems you have to consider practical feasibility. Would it turn out that for the expenditure of energy to get things isolated we may as well spend it on classical computation?

wizzwizz4 5y ago
On Earth? Maybe. In deep space? Probably not.
- evanb 5y ago
  The cosmic microwave background makes even deep intergalactic space warmer (3 or 4 K) than the inside of Earth’s best fridges (the best as low as nanoK). 3 or 4 K is easy to achieve using liquid helium cooling, which is presumably why eg. Google’s Sycamore chip operators in that range. But achieving those low temperatures is a regular occurrence in labs all over the world—-you call AirGas or somebody and they deliver a dewar of liquid He.
  - wizzwizz4 5y ago
    And, close to a star, you have several neutrinos flying through your experiment. You have vibrations from earthquakes. You have electromagnetic coupling. etc, etc. The temperatures are easy enough; you just have to compensate for thermal noise. The isolation isn't; without isolation, your signal is wrong.
    - pishpash 5y ago
      But unless you're doing a computation without I/O (i.e. no reading back the results, no providing inputs), you need coupling into the rest of the universe, and typically into a low-entropy part of the universe like the Earth, where you have entities that care about the computation. So, I am not convinced having a deeply isolated part of the universe is the answer; in fact, the isolation vs. signal quality tradeoff makes it sound more and more like a fundamental limitation of practical concern.
      - wizzwizz4 5y ago
        > But unless you're doing a computation without I/O (i.e. no reading back the results, no providing inputs), you need coupling into the rest of the universe, and typically into a low-entropy part of the universe like the Earth, where you have entities that care about the computation. With a quantum computer, you can only do that at the end of the computation. Not half-way through; that'll cause the computer to start doing a different (unwanted) computation instead. While the calculation is happening, you need (a high probability of) total isolation from the rest of the universe, so that the intermediate state of the computer only interferes with itself. > So, I am not convinced having a deeply isolated part of the universe is the answer; in fact, the isolation vs. signal quality tradeoff makes it sound more and more like a fundamental limitation of practical concern. It is a fundamental limitation of practical concern! Just like the need to keep conventional computer processors cool or they melt, or the fundamental limitations on the bandwidth that a radio frequency can give you. The people who deal with these limitations are called engineers.
deleted 5y ago
[deleted]

octoberfranklin 5y ago

> It's an engineering problem, as far as I understand. That is far from being clear. People in the 1700s were totally convinced that building a perpetual motion machine was just "an engineering problem".