I'm not always the biggest fan of quoting Wikipedia but here goes:

'Nondeterministically' guessing the answer won't be enough. There is a class called BPP that concerns those algorithms classically, quantum computing goes further, but might still not be able to solve NP-complete problems fast. You say "an NP problem is one that can be solved in polynomial time", but you either meant that the answer can be checked in polynomial time or that you know P=NP. In the last case large amounts of fame and money are waiting on you.

There is no reason to believe NP-complete problems can be solved in polynomial time (let alone constant time) on a quantum computer.

Their competitors are probably green with envy!