Re: So we're up to 56 now
56? Pretty sure 53.
Not that that's a significant objection to what Google have achieved, by the way. I've been something of a QC skeptic myself - not that I didn't believe in the published results, just that I've felt it was likely that 1) it would take a long time to achieve quantum computational supremacy, if 2) it was feasible at all. (Interested parties can hunt down some of my earlier posts for links to arguments from physicists and others supporting the latter position. I wasn't convinced, but I thought some of the arguments were at least plausible.)
And we still have a long way to go before we have a machine with enough "logical qubits" (that is, error-corrected qubits, which may well mean orders of magnitude more physical qubits) to compute arbitrary problems in BQP. The random-circuit problem Google demonstrated on Sycamore essentially returns a distribution, not an exact answer; you couldn't use a scaled-up-by-100 Sycamore to factor a 2048-bit RSA product, because it doesn't have the error correction (i.e. it has 53 physical qubits, but not 53 logical ones).
But, yeah, I have to say my predictions were wrong. It still looks like we have plenty of time to roll out post-quantum asymmetric crypto before anyone has a machine that can practically crack RSA or ECDHE, but we might have useful QC machines for things like simulating quantum processes in a few years. That's cool. (And it's nice that the Google approach is not particularly resource-intensive.)
As usual, Aaronson has some good posts. He wrote this on the IBM rebuttal, and it mentions some other critiques and links to the "quantum supremacy FAQ" he wrote when the Google paper was leaked.