The Jaynes-Cummings model describes a two-level atom coupled to a single quantized electromagnetic field mode in a cavity. The Hamiltonian H = ℏωa†a + ℏω₀σ_z/2 + ℏg(a†σ⁻ + aσ⁺) produces Rabi oscillations where excitation coherently swaps between atom and field at rate 2g√(n+1). The left panel shows the atomic inversion ⟨σ_z⟩(t) exhibiting collapse and revival — a uniquely quantum signature arising from the discrete photon distribution. Vacuum Rabi splitting 2g√n is visible in the energy level diagram on the right, where dressed states |±,n⟩ split by the coupling strength.