That's a great resource. Thanks.

The noise issue does seem problematic. Especially once you're beyond what's doable classically. I suppose that you could just check for reproducibility. But maybe there could be systematic problems that wouldn't show up doing that.

But for cracking encryption, the end results seems pretty clear. You either get sensible plaintext, or you don't. And you can try multiple times. Systematic effects that consistently yield incorrect plaintext seem unlikely.

Or am I just confused?

To my understanding, and somewhat crucially, those qubits are not error-corrected.

Those are physical qubits, not logical qubits. The blog post from Google [1] is a better (but still marketing-drenched) review. There's no research paper to read and no indication of what the precise error correction is on those 72 physical qubits. The best information we have to go on is that 1) this is a scaled up version of Google's 9-qubit quantum computer, and 2) the 9-qubit quantum computer had an error rate of 0.6%.

But in the absence of any peer review or even published material, this may as well not exist. Assuming it does exist, Google is cautiously optimistic that it will be able to demonstrate quantum supremacy. But that doesn't actually mean it will be able to do anything meaningfully useful for real world applications, it just means it will breach the threshold where it's demonstrably faster than a classical computer for something (instead of theoretically).

Once you leave the cleanroom it will be much less impressive. No one is close to developing a quantum computer capable of useful cryptanalysis. In fact, I'd confidently wager no one is even close to a breakthrough that would bring them close to the real breakthrough we need for quantum computers to break e.g. RSA. We'd need hundreds of thousands of physical qubits just to achieve the error correction requisite to break 2048-bit RSA. I'm weakly pessimistic I'll live to see it.

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1. https://ai.googleblog.com/2018/03/a-preview-of-bristlecone-g...

From the accompanying blog post https://blog.wire.com/blog/post-quantum-resistance-wire/