What does quantum computing need to move forward? Will just throwing a lot of money at the thing allow it to scale? Or are there fundamental problems blocking it that require new physics or new material sciences?
One obvious problem is cooling. We can't cool million qubits in a single fridge, so we will need to split them between fridges and communicate. Also, the wiring is really complicated already and hard to scale (one reason IBM has heavy hex is to have more space).
Another problem is connectivity. For transmon qubits connectivity is fixed. Applying gate to two far qubits requires a lot of swaps, which is expensive. This is less of a problem for ions or cold atoms because they can couple any two qubits; but they likely wouldn't be able to for large amount of qubits.
Another thing is classical control, because the classical data needs to be processed at high speed. Some companies develop specialized hardware for that.
None of these is necessarily fundamental, but these problems need to be solved, in addition to usual scaling (it is hard to manufacture these devices and it becomes harder with each qubit).
I don’t recall enough of the conversation (circa 2019) to remember anything about the properties of the problems it helps solve, so I can’t help generalize. Sorry.
Essentially, they argue that unless strong algorithmic breakthrough happens (e.g. having cubic speedup, instead of quadratic), the only practical problem for which quantum computer will be useful, are those where you get exponential speed up:simulation of quantum systems (and breaking of RSA encyrption if you count that). Even those are challenged by other (approximate) simulation by Classical Deep Learning. There will be some quantum models for which quantum supremacy will be useful and Deep Learning wont. The question what classes of systems.
I'm sure there are lots of complicated problems ahead, but i don't think we are waiting for someone to discover "new" physics.
This is not totally fair; it is possible given certain independence assumptions. But they are likely not physically realizable.
It is almost certain that even within our understanding of quantum systems it is simply not possible to have a quantum computer (much less create one). The assumptions necessary to produce a completely uncoupled system are likely invalid; we have yet to produce a compelling experiment to indicate otherwise. [1]
> Goal 3: Create distance-5 surface codes on NISQ circuits that require a little over 100 qubits.
> The argument presented in the next section asserts that attempts to reach Goals 1-3 will fail.
Goal 3 is exactly what Google has recently achieved with Willow. Actually, they did even better, reaching a distance-7 surface code (with a little over 100 qubits). Q.E.D.
To be clear, I do think your article is interesting and was valid at the time, but it goes to show how fast the field is advancing.