Action of unitary operators on qubits can be understood as rotations of the Bloch sphere representing qubits.
A basic tool in the above representation are properties of quaternions.
The inscription on the Broom Bridge in Dublin where quaternions were born.
Niles Johnson's lecture on the stereographic projection (slightly different from ours), Hopf fibration and quaternions.
Remarkable interactive visualization of quaternions and the stereographic projection
https://eater.net/quaternions
