  We analyze a prototypical particle-in-a-box model for a hole spin qubit. This
quantum dot is subjected to static magnetic and electric fields, and to a
radio-frequency electric field that drives Rabi oscillations owing to
spin-orbit coupling. We derive the equations for the Rabi frequency in a regime
where the Rabi oscillations mostly result from the coupling between the qubit
states and a single nearby excited state. This regime has been shown to prevail
in, e.g., hole spin qubits in thin silicon-on-insulator nanowires. The
equations for the Rabi frequency highlight the parameters that control the Rabi
oscillations. We show, in particular, that [110]-oriented dots on (001)
substrates perform much better than [001]-oriented dots because they take best
advantage of the anisotropy of the valence band of the host material. We also
conclude that silicon provides the best opportunities for fast Rabi
oscillations in this regime despite small spin-orbit coupling.
