[erichocean]

> It’s like, if you believed that useful air travel was fundamentally impossible

Uh, there are birds. Literally everyone thought useful air travel was possible, and not only possible, but so easy that a Darwinian process was able to produce it, not once, but literally thousands of times, in thousands of ways.

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But looking at the actual "experiment", I don't count that as computation in any meaningful sense, and morally equivalent to the following:

Set up a digital camera and point it at a scene. Take a picture. Now take millions of additional pictures, without moving the camera.

Measure the values at each pixel. See how they correspond to "amplitudes"? That's our computation. <= (This is the part of the article that should raise eyebrows...)

Article (smugly): How about you simulate (render) the scene using an actual computer? Measure the amplitudes of the resulting millions of images. OMG, that took you so long!!! Loser.

Are we being punk'd here?

The digital camera is the quantum computer. The "scene" is the random initial state C. The scene is then translated into a renderable scene for the classical computing version, and rendered with an unbiased physically based renderer, which produces the same result.

I fail to see how any of this is even remotely exciting, much less interesting. A camera is not a computer, no matter how many measurements you make with it, nor how "random" the scene you are taking pictures of is.

And yes, simulating reality takes more cycles than just measuring whatever happened with a camera. Photos are "faster" to get than the equivalently rendered scene—news at 11!

Again: Are we being punk'd here?

[alanbernstein]

I have no comment on the QC claims, but regarding the flight analogy, it seems you're being disingenuous: https://www.xaprb.com/blog/flight-is-impossible/

[erichocean]

Curious: Did you Google that just now, in order to comment here?

[simias]

You wouldn't be any less wrong if he did, I don't really see how that's relevant.

You can find other contemporary counter-examples too, for instance nuclear fusion. We know it's possible, it exists in nature, we managed to do it under very special conditions but it's still unclear whether it's actually possible to build a competitive, safe commercial nuclear fusion reactor.

[alanbernstein]

Yes I did. Did you invent a historical "fact" to comment here?

[core-questions]

Perhaps it will make more sense to explain how a D-Wave machine works, as (a) they actually exist and you can use one today for free online, and (b) it's way simpler than a gate model QC is.

Imagine a bunch of magnets. Imagine forcing them into a "frustrated" configuration; maybe you have them all on a grid, and you have servomotors that can rotate them to face any way you like. The servomotors are strong, so counteracting the magnetic forces is easy for them. You design an appropriately frustrated configuration, and then release all of the magnets at once. What configuration do they rotate into?

A quantum annealer is conceptually similar. Each qubit, on a regular, patterned graph, has connections to its neighbours. You can leave these alone (no corellation) or tune them up to +/- 1, corresponding to "must be the same as this other qubit" and "must be different than this other qubit". You can also bias each individual qubit to be a 0 or a 1.

Then, you let it go, and it anneals, and you observe the result. Your goal is to get to the _lowest energy state_ possible: the least possible frustration remaining.

In our magnet example, it would be as few magnets as possible wanting to move - if you poked them with your finger they'd want to go back into their current state. You could imagine that your magnets might not get down to their absolute lowest energy state; maybe it would take too much energy to flip from their starting state to that lower state. In a quantum system, because of tunneling, the system can reach these lower ground states. Rather than being in a fixed position the way our magnets were, qubits are in a quantum superposition, so they can reach a lower energy state without having to climb up that energy hill. Or so we're lead to believe by the numbers, anyway; I'm not a physicist.

Now, if you can map some useful computational question onto the original configuration of qubits that is answered by the ending position, you've got yourself a useful quantum computer. This is the hard part! The key is to use optimization algorithms where a lower energy state = a more optimized result. If you can do this, there's a ton of employment waiting for you.

Then, if you want "quantum supremacy", it's matter of providing more optimized answers in less time, particularly as the problem scales up in complexity. There does indeed appear to be a crossover point coming in a decade or so, at least for the small class of real-world problems that the Ising Hamiltonian works for.

[erichocean]

> Now, if you can map some useful computational question onto the original configuration of qubits that is answered by the ending position, you've got yourself a useful quantum computer. This is the hard part!

Yes, I agree. But this has not been demonstrated. What's being demonstrated (apparently) is that measuring a quote-unquote "quantum computer" doing whatever it does naturally is easier than simulating said quantum computer classically. Well, yeah. Duh.

That's the same thing as "rendering" a scene with an unbiased renderer vs. setting up that same scene in reality and using a camera. No one in their right mind would point to the camera and say they'd create a next-gen, heretofor impossibly fast unbiased rendering algorithm.

Technically, the digital camera is "computing" the same result—but no one would call it that, and IMO, the same is true of what is being discussed in the FAQ. It's literally NOT COMPUTATION, which brings us back to your line:

> Now, if you can map some useful computational question onto the original configuration of qubits that is answered by the ending position, you've got yourself a useful quantum computer. This is the hard part!

It's not only the hard part, it's the only part that matters. Until then, you have AT BEST a "quantum camera". Potentially useful, perhaps—but it's not a computer, or computation.

Anyway, thanks for responding. Much better than drive-by downvoters probably hoping to get PhDs in this stuff.

Also, my intent is not to belittle Google's engineering effort. In the same way that I wouldn't belittle Sony for making 24mmx36mm backlit CMOS sensors. It's impressive! Good for them. But it's not computation, and it definitely doesn't establish some kind of "quantum computing supremacy" (since no meaningful computation is being done). When they stop handwaving about mapping actual computation problems to the scene they've set up and are measuring, then I'll get excited. Maybe it's doable, maybe not. But a quantum camera, AT BEST, is one step along the path...

[jeeceebees]

I think your camera example is a false equivalence that makes this seem as if it's not a computation. The camera is not running the same algorithm as the renderer and so you're comparing different things.

The experiment used a classical computer to randomly generate a circuit C, told the quantum computer to execute it, and recorded the result. Then they repeated this but executed each circuit in the most optimal way a classical computer can. Finally they compared the distributions to verify that the quantum computer's results matched the correct classically computed results.

This proves that the quantum computer is able to generate that distribution faster than a classical computer and isn't just doing some other spurious process that happens to be faster.

Yes, this random distribution isn't very useful and so this result is only really interesting as an experimental verification of theory. However, it is a computation that benefits from quantum speedup in real life!

Hopefully soon, algorithms will be found to generate more useful distributions (as it seems for the time being sampling is the only application of this type of QC that is practically doable). For example, Aaronson mentions that generating verifiably random bits is not much more difficult than the noise generated in this experiment and could have an impact in a variety of cryptographic applications.

[erichocean]

> The camera is not running the same algorithm as the renderer and so you're comparing different things.

[rewriting your words] The experiment used a classical computer to randomly generate a scene C, set that scene up in real life, and recorded the result. Then they repeated this but rendered the scene in the most optimal way a classical computer can. Finally they compared the results to verify that the scene in real life matched the correct classically computed results.

The scene + digital camera has the exact same role (and proof value) in my hypothetical experiment as the quantum computer + measurement device does in the Google experiment.

It's not the camera that "contains the circuit", it's the scene and the camera together that computes the same values (exactly, as it turns out) as the classically computed rendering algorithm of the same phenomena.

Call it "camera computing", write a paper in Nature, win Turing award. The hard part with camera computing is the same: How to map a computation onto the generated scene so that the measurement device (camera) gets a meaningful result faster than it can be simulated in the computer.

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Look, I've worked on things for a long time only to discover in the end that there's nothing there. It sucks, I get it. Move on, try something else. There's nothing here.