Nothing supernatural. It may help to understand that a prime motivation for building quantum computers is that they provide the only known way to perform quant

Nothing supernatural. It may help to understand that a prime motivation for building quantum computers is that they provide the only known way to perform quantum mechanics calculations of general physical systems at significant scale. In other words, although you can simulate a quantum computer in principle, and calculate the effects of the laws of quantum mechanics in principle, in practice classical (non-quantum) computers hit a computional wall doing either of those things above a certain level of complexity which occurs in the natural world. That makes it impossible to work backwards from physical observations of sufficiently complex systems to confirm that the underlying process is following the laws of quantum mechanics as we currently formulate them. Basically, we need a quantum computer to do the kinds of calculations needed to relate physics observations of complex quantum systems to their quantum mechanics underpinnings. We just can't do the math otherwise. Quantum mechanics itself has been verified to extraordinary precision over a wide range of phenomena. We know the physics and mathematics works and is remarkably accurate, for the things we can test. That includes many macroscopic observations; it's not a size problem. We have all sorts of clever ways of calculating different kinds of physics observations from underlying quantum mechanics. But the calculations are all limited in the quantum information complexity they can handle, in practice. In particular, nothing with the high level of coherent but complex quantum state required for a substantial size quantum computer is calculatable without a quantum computer, as far as we know. So, remarkably, quantum mechanics being verified over a wide range of phenomena isn't enough to tell us if quantum computation at significant scale is possible, because we can't do the calculations that show if the observed universe is following mathematical quantum mechanics closely enough to support one. Ironically, to measure if the universe supports quantum computation, we have to build a quantum computer just to be able to do the calculations that show us if we can build a quantum computer.