[apt-apt-apt-apt]

AIUI, the scientists achieved a self-sustaining nuclear chain reaction around 1943. That was the hard part, not even a small bomb yet, but a bomb just needed more fuel and scale.

Fault tolerance is the hard part for QC, once it's achieved, the difference between factoring 35 and RSA-2048 is an engineering challenge, not an impossibility.

[nickelpro]

Fault tolerance is a hard problem, assembling qubits for simultaneous gate operations is another hard problem. There are several dozen others.

It is exceptionally unlikely CRQC will be achieved in our lifetimes, if ever. The closer example is economically-viable fusion power production, which today has better odds than CRQC but remains solidly in the "maybe" zone after decades of global investment. Even though fusion weapons had been achieved half a century beforehand.

The bombs were actually relatively easy problems, in the scheme of things.

It is never wise to listen to people who's jobs and funding are connected to the development of a technology on when that technology will arrive. The answer is always "soon".

[tempay]

Fusion also came to my mind but after thinking about it for longer I think it's a bad argument. The challenge with fusion is mostly around scale and efficiency to make it competitive against other energy sources (and net energy positive in the first place).

For CRQC it doesn't matter if they're massive expensive energy monsters. Even being able to break a single chosen key is enough to be a problem and once you can do one you can definitely do ten or a hundred.

[nickelpro]

They're just different definitions of success.

For fusion the bar is "economically viable", in the current discussion for QC the bar is "cryptographically relevant".

They are comparable in that to meet either criteria, a variety of unsolved engineering challenges need to be overcome. For both, some of those problems have no clear and obvious solutions to which a simple application of resources and time will achieve.

Currently unknown innovations are required, unknown unknowns lurk in the dark corners, and all projections are relying on the assumption such innovations will arrive in a timely fashion and the unknown unknowns will be harmless glitches.

Neither are likely impossible, but betting on timelines is a fools game. This isn't the NYT publishing man-made flight is a million years away 2 months before the Wright brothers flew at Kitty Hawk, waiting for the right conglomeration of otherwise sound engineering to materialize in one place. It's like saying level 5 self-driving cars are two years away, a perpetually delayed technology for which all problems are well known and no new innovations are imminent.