A spin-1/2 state |ψ⟩ = α|↑⟩+β|↓⟩ precesses on the Bloch sphere under H = −½ω₀σ_z + ½Ω_R σ_x (lab frame). Rabi oscillations: |⟨↑|ψ(t)⟩|² oscillates at the generalized Rabi frequency Ω = √(Δ²+Ω_R²).