Dyakonov writes: "With what exactitude must, say, the square root of 2 (an irrational number that enters into many of the relevant quantum operations) be experimentally realized? Should it be approximated as 1.41 or as 1.41421356237? Or is even more precision needed? Amazingly, not only are there no clear answers to these crucial questions, but they were never even discussed!” This reminds me of Reagan’s quote that there is no word in Russian for freedom… It’s true that Hilbert space is high-dimensional, and an n-qubit system is specified by 2^n complex amplitudes. But as Brent quotes Feynman, nature has no problem keeping track of them all. And it’s not true that quantum algorithms require us to control or observe this many variables: we only observe (squares of) linear combinations of them. Noise and precision gets discussed in quantum computing quite a bit. The “fidelity” of a quantum gate is the inner product between the resulting state and the intended one. Typical gate fidelities now are 0.99, which roughly means we can do 100 quantum gates before the calculation fails. It’s true that we need to get much closer to 1 before we can do quantum error correction and sustain computations of arbitrary length, but I think this is an engineering problem, not a fundamental one. In the meantime, we already have devices which are pushing beyond our ability to simulate or predict them classically. These devices fall far short ot implementing e.g. Shor’s factoring algorithm, but they are radically new physical objects that deserve study in their own right. - Cris
On Nov 21, 2018, at 2:20 PM, Dan Asimov <dasimov@earthlink.net> wrote:
I am a complete ignoramus about quantum computing, so this article roughly doubled my knowledge of it.
I will say this: That article by Mikhail Dyakonov is *extremely* clear and well-written.
—Dan
Hans Havermann schrieb: ----- In the IEEE Spectrum last week, Mikhail Dyakonov presented his overview of the field:
https://spectrum.ieee.org/computing/hardware/the-case-against-quantum-comput... -----
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