On the Wikipedia page for quantum algorithm I read that
[a]ll problems which can be solved on a quantum computer can be solved on a classical computer. In particular, problems which are undecidable using classical computers remain undecidable using quantum computers.
I expected that the fundamental changes that a quantum computer brings would lead to the possibility of not only solving problems that could already be solved with a classical computer, but also new problems that could not be solved before. Why is it that a quantum computer can only solve the same problems?