Quantum computation is no different than classical, except the bit registers have the ability to superpose and entangle, which allows certain specific algorithms like integer factorization to run faster. But conceptually it's still just digital code and an instruction pointer. There's nothing more "physical" about it than classical computing.

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daxfohl 3 months ago | parent [-]

And it's definitely not "try every possibility in parallel", as is sometimes portrayed by people who don't know better. While quantum computing makes it possible to superpose multiple possibilities, the way quantum mechanics works, you can only measure one (and you have to decide ahead of time which one to measure, i.e. you can't ask the quantum system like "give me the superposition with the highest value"). That's why only a few specific algorithms are aided by quantum computing at all. Integer factorization (or more generally, anything that uses Fourier transforms) is the biggest, where it's exponential speedup, but most others are just quadratic speedup.

And even if you could simulate and measure multiple things in parallel, that still wouldn't let you solve the halting problem, which would require simulating and measuring infinite things in parallel.

Another way of saying it: everything that can be done on a quantum computer can also be done on a classical computer. It's just that some specific algorithms can be done much faster on a quantum computer, and in the case of integer factorization, a quantum computer could factor numbers larger than would ever be practical on a classical computer. But that's really it. There's nothing magical about them.

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randysalami 3 months ago | parent [-]

“Nature isn’t classical, dammit, and if you want to make a simulation of nature, you’d better make it quantum mechanical, and by golly it’s a wonderful problem, because it doesn’t look so easy” (Richard Feynman). Quantum systems are physical systems, classical systems due to their very nature only can emulate it. When it comes to agents like we were discussing before, a classical agent will always be limited by the abstractions needed to get it to understand the real world. A quantum agent would actually “get” the world. The difference is fidelity and classic systems will only ever be an approximation.

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daxfohl 3 months ago | parent [-]

This is irrelevant. First, quantum programs don't "get" anything just by virtue of being quantum code, any more than classical computers "get" the foundations of electricity and magnetism because they use electrons. Second, classical computers absolutely can simulate quantum systems. They're inefficient, but they can do it. Third, determining whether an agent is stuck in an infinite loop has nothing to do with the physical world. They're just binary code running on a Turing machine. Fourth, the halting problem is provably unsolvable in both classical and quantum systems, so there's not even a relationship here. Fifth, what do you mean by quantum systems are physical? Does this mean classical systems aren't? Are physical systems only those that use every aspect of physics? Then quantum systems aren't physical either because they can't account for gravity. So do we need quantum gravitational computers? Sixth, what does "getting" quantum mechanics that have to do with AI agents? Do I need to understand quantum physics before I can have a conversation with someone? Can I not read an email without an appeal to hilbert space? Just, none of this is related to quantum computing. It's like having a bug in a deployment and saying string theory would've prevented that.

	▲	daxfohl 3 months ago \| parent [-]
		I see intermixing of the terms quantum computer and quantum system. These are different concepts, and I think that's the source of the confusion. A quantum computer is a well defined thing. It's just like a classical computer but instead of just binary bits, it can work with qubits that support superposition. But it still needs programs just like a classical computer, and the results that we can actually read are binary in both cases. Both of them are quantum "systems", in that both require quantum physics to work, if we're considering modern CPU gate sizes. Just, classical computers expose binary bits, and quantum computers expose qubits. What I think you're picturing is a quantum "system", like a blob of quantum goo, that you can toss some "state" into and...something. But, that's not what a quantum computer is, any more than a classical computer is something you could throw into a blob of electrical goop and expect it to do anything.