Complex numbers just allow you to add a dimension to real numbers (so think vectors) while allowing handy operations (rotations). So they end up being useful in

Complex numbers just allow you to add a dimension to real numbers (so think vectors) while allowing handy operations (rotations). So they end up being useful in all sorts of places, although you don’t have to use them. An n qubit quantum computers allow you to “visit” 2^n states but to to store only a few states. A n bit computer allows you to store 2^n states but to visit only a few states (for n large)