Quantum computers are exceptionally costly to build and only a couple of nations have shown interest in it! If you think hackers will use such computers to launch an attack on cryptocurrencies like bitcoin, then you are daydreaming. Quantum computing is not yet a threat to cryptography, at least not now and not in immediate future!
Actually they've started to also build 5000$ quantum computers too. Of course, they are very weak (2 qbit) hence they don't need liquid helium for cooling.
And I think that you are also wrong about government financed quantum computers. In the same way super computers were used for crypto mining by this or that scientist with access to them, I can also expect this kind of "accidents" happen now and then with quantum computers too in the future.
But from what I've read (since there are plenty of threads here on this topic!) Bitcoin is pretty much safe from quantum computing and the only weakness (albeit theoretical) may be in the address reuse. (If I understood right). However, there are a lot of things in this world protected by cryptography, same or weaker than Bitcoin's, if this is hacked the problems will be .. generalized.