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Transistors, plants, hands, and tables are all macroscopic. We see quantum mechanical effects, but we do not see stable superpositions. None of these real-world

Transistors, plants, hands, and tables are all macroscopic. We see quantum mechanical effects, but we do not see stable superpositions. None of these real-world examples seem to shield a quantum state from decoherence in the way a quantum computer needs to. The sun demonstrates clearly that fusion is controllable (albeit in a regime we struggle to match). I don't think your examples show that a quantum state can be controlled at the scale we need it to be, and I don't know of any extant phenomena that do. But I am no expert, yell at me if I'm wrong.

krastanov 1y ago
On the contrary, we have plenty of examples of long-lived (many hours, days, or more) examples of superposition in many solid state materials and chemical systems. For a quantum computer you need both (1) something that can retain superposition and (2) be easily controllable. Point 2 is the difficult one, because if you can control it (interact with it), the "environment" can interact with it and destroy it as well. All of the examples of macroscopic effects above are possible thanks to effects explainable only through the existence of superposition. It is just that they are not particularly controllable and thus not of interest for storing quantum information. Another fun point: the example you are focusing on, fusion happening in the sun, is only possible due to the quantum tunneling effect, which is itself dependent on "superposition" being a real thing. Looking past the clouds at our star is already an example of quantum mechanics working, which is very much an experimental observation of an effect possible only thanks to the existence of superposition.
- walleeee 1y ago
  Thanks, I'll stand partially corrected. It was a badly written comment, or muddled thoughts, or both. I didn't mean to doubt the existence of superposition or our ability to achieve it for sustained periods. But doesn't the point stand? I meant to say that none of the examples seem to demonstrate both 1) and 2). Do we know of any natural system which can maintain and precisely manipulate a quantum state like a quantum computer needs to?
  - immibis 1y ago
    Well no, but we also don't know any natural system that does fusion using an amount of material smaller than about a billion billion billion tonnes. Getting from A (what we know works) to B (what we'd like to work) is the hard problem. That's called research.

krastanov 1y ago

On the contrary, we have plenty of examples of long-lived (many hours, days, or more) examples of superposition in many solid state materials and chemical systems. For a quantum computer you need both (1) something that can retain superposition and (2) be easily controllable. Point 2 is the difficult one, because if you can control it (interact with it), the "environment" can interact with it and destroy it as well. All of the examples of macroscopic effects above are possible thanks to effects explainable only through the existence of superposition. It is just that they are not particularly controllable and thus not of interest for storing quantum information. Another fun point: the example you are focusing on, fusion happening in the sun, is only possible due to the quantum tunneling effect, which is itself dependent on "superposition" being a real thing. Looking past the clouds at our star is already an example of quantum mechanics working, which is very much an experimental observation of an effect possible only thanks to the existence of superposition.

walleeee 1y ago
Thanks, I'll stand partially corrected. It was a badly written comment, or muddled thoughts, or both. I didn't mean to doubt the existence of superposition or our ability to achieve it for sustained periods. But doesn't the point stand? I meant to say that none of the examples seem to demonstrate both 1) and 2). Do we know of any natural system which can maintain and precisely manipulate a quantum state like a quantum computer needs to?
- immibis 1y ago
  Well no, but we also don't know any natural system that does fusion using an amount of material smaller than about a billion billion billion tonnes. Getting from A (what we know works) to B (what we'd like to work) is the hard problem. That's called research.