Past exam of the laser science and quantum information processing course of the University of Oxford / 2021 / 3 / b / iii / Solution

A resonant Rabi pi pulse givesIt swaps $|0⟩$ and $|1⟩$ with a common global phase, implementing the Pauli gate $X$, or NOT. Its Bloch sphere action is a half-turn about the $x$-axis.