On Wed, Oct 6, 2021 at 6:10 PM 'Brent Meeker' via Everything List < [email protected]> wrote:
*> here are only about two dozen problems for which there is a known > quantum algorithm faster than the best classical algorithm* > True, but considering the fact that we don't have a working quantum computer that programmers can use to try out ideas and tweak things it's a wonder we have any quantum algorithms at all. Imagine trying to write a large complex computer program in hexadecimal with just pencil and paper and no computer; it might not be exactly impossible but it would sure be hard as hell, and I doubt it would run perfectly the first time it was actually tried out on a real computer. > ..*.and even there "faster" means in the limit of large problem size, not > necessarily in realistic problem sizes. * > All the applications in which quantum computers are substantially superior to conventional computers are problems in which a very small increase in problem size results in a gargantuan increase in the number of computations required for a solution; and such problems turn out to be the norm not the exception in our real physical world. Nearly a century ago Niels Bohr was able to calculate from first principles the spectrum of the simplest element hydrogen, but because the calculations became too complex he couldn't do it for the second simplest element helium, and even today we can't do much better. From first principles no conventional computer can calculate, even approximately, what a large organic molecule will do, but a quantum computer could. > *> And when you talk about practical computers, how much more would it be > worth to you if the word processor on your laptop was a thousand times > faster* > Word processing on a quantum computer is like killing a fly with a sledgehammer, nobody is suggesting that. A 100 Qubit quantum computer could make far more computations than all the conventional computers on Earth combined, but only if those 100 Qubits were nearly perfect; that's why quantum error correction is so important; it might take over a 1000 imperfect physical Qubits, or maybe only a few dozen, to make one nearly perfect logical Qubit that can be used in computations that will change the world forever. I have little doubt that when working quantum computers become available, quantum error correction schemes will be developed that are superior to anything we have now. *> The "practical" applications were initially supposed to be in > encryption, both breaking and making unbreakable. * > I always thought cryptology was just a trivial application of quantum computers and that the real killer application was the simulation of quantum systems. > > * > But now all the financial institutions are switching from RSA to > encryption for which there's no QC algorithm to break it.* > I assume you're talking about lattice-based cryptography, and it's true there is currently no QC algorithm to break it, but I wouldn't be too confident that situation will never change once quantum computers become available and cryptographers really try to break it. And nobody has devised a lattice-based system that is practical, the key it uses is HUGE and it's s-l-o-w, it would take so long to use a credit card to buy something on Amazon that people would lose patience, the company would go out of business, and brick and mortar stores would come back in style as would paper money. John K Clark See what's on my new list at Extropolis <https://groups.google.com/g/extropolis> nqx -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/CAJPayv1-Ne10RYikpfR5sf4VHJN9WBd8_92YfE8EjjtWcjymKQ%40mail.gmail.com.
