$BTC

Nothing is perfect, the quantum processor could destroy cryptocurrencies and all electronic security known to date....

The Bitcoin network is more secure as long as it has more miners (speed).

One single quantum processor would have more speed than all the miners combined.

Thus, the 51% blockchain attack would be possible. (Search on Google what the 51% attack is). It has already been tested and achieved on the ETHEREUM CLASSIC NETWORK ($ETC )