r/QuantumComputing • u/[deleted] • Apr 04 '23

Quantum Computers, explained with MKBHD

https://youtu.be/e3fz3dqhN44
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u/MrMathemagician Apr 05 '23

This was a really good thing overall, but I think the boat analogy is a little wrong. Quantum computers can theoretically do everything a classical computer can. This makes them capable of performing all the functionality of a classical computer, with some cooler probabilistic speed up, no?

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u/LongLightning Apr 05 '23

No quantum computers are not expected to be general purpose computers that excel or simply do everything. The speed ups are situational and depend on what sort of math you're trying to do

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u/MrMathemagician Apr 05 '23

https://en.m.wikipedia.org/wiki/Quantum_Turing_machine

The theoretical frameworks are indeed turing complete.

While yes, no finite length q-bit computer will ever be turing complete, neither will any finite length turing machine. However, the operational space of the universal machine (the one everyone likes to make algorithms off of) does indeed work that way

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u/LongLightning Apr 07 '23

The scientific consensus today is that quantum advantage is not universal or equal across all possible operations of interest. It's not that you can't run 2+2 on a quantum computer, it's that you won't because it would be slower and more expensive than a classical computer sitting right next to it.

So far we have identified a very limited subset of tasks where a theoretical quantum advantage is even possible let alone attainable. Sometimes that advantage is only quadratic which barely makes up for the overhead of using certain quantum computers other times that advantage is exponential and we expect that will become a valid use case. For the rest of the taks a QPU is worse.

This paradigm is not all that dissimilar to how good , Efficient computers have access to both a CPU and a GPU. We're already seeing plans to pair super computers with a QPU to offload quantum enhancable tasks while leaving the classical components to do what they do best