Willow quantum chip demonstrates verifiable quantum advantage on hardware

Can someone explain if this is still the RCS problem or a similar one?

My impression was that every problem a quantum computer solves in practice right now is basically reducible from 'simulate a quantum computer'

This is not the RCS problem or indeed anything from number theory.

The announcement is about an algorithm which they are calling Quantum Echoes, where you set up the experiment, perturb one of the qbits and observe the “echoes” through the rest of the system.

They use it to replicate a classical experiment in chemistry done using nuclear magnetic resonance imaging. They say they are able to reproduce the results of that conventional experiment and gather additional data which is unavailable via conventional means.

This is quite different from their previous random circuit sampling (RCS) experiments that have made headlines a few times in the past. The key difference from an applied standpoint is that the output of RCS is a random bitstring which is different every time you run the algorithm. These bitstrings are not reproducible, and also not particularly interesting, except for the fact that only a quantum computer can generate them efficiently.

The new experiment generates the same result every time you run it (after a small amount of averaging). It also involves running a much more structured circuit (as opposed to a random circuit), so all-in-all, the result is much more 'under control.'

As a cherry on top, the output has some connection to molecular spectroscopy. It still isn't that useful at this scale, but it is much more like the kind of thing you would hope to use a quantum computer for someday (and certainly more useful than generating random bitstrings).