It is known that it's not technologically impossible. There are ways to do it, some of them rather outlandish but not infeasible.
Unfortunately, that's as far as it can go. Either you start doing something really extreme to ensure that players can't cheat (that aforementioned strip search, making them play in a Faraday cage, etc), you'll never really know.
Even worse than that, the cheating may not have gone on during the match. It could have been as simple as old-fashioned spying: studying what preparations Carlsen had made, and learning their weaknesses before the match even starts.
You can't really prevent that. The best you can hope for is for a chess expert to opine that this move seems like an unlikely thing for a human to play without the assistance of a computer. Carlsen is just such an expert, but obviously his opinion alone is much too biased.