[fooker]

We do not know that actually. While it might be true that classical mechanics is the only machine behind our brain, evolution is just as likely to have stumbled into a quantum computer design we have not yet discovered in the last billion years.

[Filligree]

Quantum computers still can't solve NP-complete problems in polynomial time, sadly. Take a look at the BQP complexity class; it's only a subset of NP.