What exactly is quantum computing? Like can someone eli5?
this post was submitted on 19 Dec 2023
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Quantum computing is going to make it possible to solve problems that normal computers simply cannot do.
Most of these are optimizing problems like "compute the best solution to traveling salesman" or "find a molecule that binds to this receptor".
On normal computers solving such problems "perfectly" takes^exponential^ amount of computing time vs. the size of the problem.
Quantum computers are going to chop down that exponential thing a little, so we can see the results before the sun burns out. The reason QCs are theoretically able to do this is that each added qubit improves the machines performance exponentially.
However, the qubit state is so fragile that we need hundreds of them to make a single "stable" logical qubit that can do operations repeatedly. What the quantum computer uses as qubit (photons, super-conducting wire) is irrelevant as long as the system can do useful work.
Because of the fragility, the results are gathered using thousands of runs on the quantum machine and measured statistically.
We are not quite there yet to solve any useful sized problems.
Is there actually a quantum algorithm that makes the traveling salesman problem tractable?
"traveling salesman problem quantum annealing" produces results on arXiv.org, so the math heads are hard at work. :)
Classical Computers count numbers and do math on numbers. Quantum Computers count collections of numbers and do math on entire collections of numbers.
One is like cooking a full course meal on a single stovetop, the other is doing the same but using an entire restaurant kitchen. The end result is the same meal, but the approach was different. The home chef classic computer has to cook things in the order they were served in, but was able to clean dishes and prepare each step. Problems could be identified and fixed swiftly, buIt took a long time and there were probably a lot of delays between courses so it wasn't the best meal and a lot of shortcuts and hacks are done to keep things moving.
The restaurant chef does the whole thing all at once and staggers cook timings so everything arrives at the right time. They have no time so they need to carefully plan ahead and set things up, then they have to burn through a shitload of energy making the meal. If anything goes wrong, the whole thing collapses. It may take a higher level of skill to make the meal, but that skill is still founded on the core principles found at home cooking and can even be used at home in a limited manner.
Technically quantum computers can't do anything new, but the speed boost allows us to do things that are currently impossible. Doing more math at the same time in huge batches is the compututational speed equivalent of breaking the sound barrier.
Computers only operate with a 1 or 0. Quantum computing is the ability to have multiple values between 1 and 0. This allows for more complex calculations to be done with less steps.
My understanding is it's much better with working with probabilistic problems. Something that could take a trillion years to guess with a traditional computer could be done reasonably fast with a quantum computer.
To my understanding Its like regular computing but better in doing specific things and worst at other stuff.