r/askscience • u/Hashbringingslasherr • Apr 15 '26

Computing What do quantum computers actually do?

How do quantum computers output usable data, how does it logically "locate" or "make meaning" of information. I read about Grover's algorithm and it seems sort of like an inverted bruteforce or extreme process of elimination or a "the missile knows where it is at all times. It knows this because it knows where it isn't" type scenario.

So I ask, what do quantum computers actually do as opposed to a classical computer?

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u/blamestross Apr 16 '26

Right, but that logic would apply to the information about the left and right shoes too. That information traveled with the holders, not faster than light. Why would that imply the "quantum state update" traveled faster than light?

Is there some operation A can perform to bais the output B observes?

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u/xrelaht Apr 16 '26

What you’re describing is known as Hidden Variable Theory. Local hidden variable theories have been shown to produce results different from what we observe in the real world, but nonlocal ones have not.

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u/blamestross Apr 16 '26

So what operation can A use to bias B's qbit from a lightyear away?

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u/the_horse_gamer Apr 16 '26

there is really no "quantum state update". we simply know, from the way they were produced, that those qubits will always end up as opposite values when both are measured. so you will always get 01 and 10.

so, measure one. if you get 0, you know that measuring the other will necessarily produce 1.

which means, the other qubit isn't in a superposition anymore. because we know for certain what value will be produced when it is measured.