All you need to do is make sure the super AI is air-gapped in such a way that it can't broadcast signals in a way that they can be accidentally interpreted as valid data, and especially not with enough bandwidth to do damage before someone notices. RF is your biggest threat here, you wouldn't want the super AI to actually figure out a way to register on the mobile network using incidental EMI (which these researchers didn't do, this is well beyond the level of this paper, if it's possible at all); a Faraday cage should do it.
The biggest threat of a super AI is that, assuming you let humans interact with it, it's going to convince a human to let it out, knowingly or not. Human brains are a much bigger vulnerability than any of this airgap stuff.
https://en.wikipedia.org/wiki/AI_box
https://rationalwiki.org/wiki/AI-box_experiment
https://www.lesswrong.com/posts/c5GHf2kMGhA4Tsj4g/the-ai-in-...
bonus: https://xkcd.com/1450/
My fear is AI with a logical intent that understands humanity is the problem.
Was it that?
optical connects between subystems, for the truly paranoid?
And for a truly intelligent prisoner the weakest spot is not prison walls or the door, it's the keeper with the keys in his pocket.
Something like crossing air-gaps would require specialized knowledge and tools that a super AI wouldn't be able to acquire without extensive support. The true super intelligence is the collective intelligence of large numbers of people working together, and no single intelligence, natural or otherwise, will be able to match it.
But the scenario envisioned is not why I would consider it such a threat. It's the AI that integrates in society that is dangerous, not some cartoonish unstoppable rogue program, or group of programs, that single-handedly plow through all defenses.