Quantum computers can solve certain problems faster than classical computers e.g factoring numbers.
and this is because quantum computers can do a fourier transform on $n$ qubits in $O(n^2)$ time as opposed to $O(n2^n)$ time.
We can usually reduce time complexities by pretending that we can do some thing faster - introducing oracle's that can solve a problem instantly.
Is there a constant time oracle that encodes all the quantum speed ups we get?