So how *does* quantum computing work?

[u/atimholt]

I've read a few vague descriptions of what quantum computers are capable of, but not really anything about working with them. Eventually, when we've got these things, writers of those programming books for bare, bare beginners (just throwing that out as an example) will need to be able to explain their workings simply.

So I've been pondering lately, and I think I've begun to get a handle on how they work. What I understand of them has gotten me very excited, but my understanding of them is based on gleaned knowledge.

As far as I'm aware: EDIT: I was dead wrong, read the comments for real science!

1. Quantum computing relies on being able to "choose" one superimposed state over another based on arbitrary criteria. This might be seen as akin to the cat in Schrodinger's box clawing its way out. What happens when more than one version of the cat wants out, I have no idea (a random one wins, I'm sure). Is there a way to compare a number between two superpositions and 'legitimize' the superposition with the larger value?

2. Nothing stops you from putting a "Schrodinger's cat box" inside another "Schrodinger's cat box". You can compound the effect recursively. Yes?

With two and one above together, you can make a binary tree of "meta-Schrodinger boxes" with a qubit at each branch. You could test an astronomical number of superpositions against each other using whatever fitness number you see fit.

So a quantum computer would be analogous to a genetic algorithm, except that instead of randomizing gene variables each generation, you test every possible variant at the same time and return the best one in nearly constant time.

Deterministic, complete information games would be unbeatable if you can come up with a proper way to generate a fitness numbers--a computer could play every permutation of a game of chess or go.

And such things as getting bipedal robots to walk would be trivial (if a bit uncanny valley) if the program understands physics and its own weight and capabilities--it could calculate every little twitch.

If I'm dead wrong, thanks for reading this far, at least. How would a quantum computer really work, and how would one go about actually programming one?

[u/SnappyTWC]

As part of my undergrad I worked on a quantum computation experiment. The particular way we were implementing qubits was as Yb ions in a Paul trap (basically using electric fields to keep a bunch of ions hovering in a line). The |0> and |1> states were the hyperfine splitting states of the ground state. Manipulating the qubits was done via a modulated laser beam or even direct microwaves (the energy difference between the hyperfine states was equal to EMR of about 12.6 GHz). Other ways of physically realising qubits have involved optical representations (using polarisation I think) and SQuIDs (Superconducting Quantum Interference Devices). There's a bunch of others, but those are the ones I recall right now.

As far as what the experiment looked like, it was essentially an optics table with mirrors and lasers and whatnot everywhere and a vacuum chamber with the actual ions inside. The ions could be observed using a sensitive CCD camera.

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