Dicke model: N two-level atoms coupled to a single cavity mode with coupling λ. Drive (pump) and dissipation (decay κ, γ) create a non-equilibrium steady state. Superradiant transition: at λ_c = √(κγ)/2 (for equal coupling), the field amplitude ⟨a⟩ bifurcates from 0 (normal phase) to nonzero (superradiant). Bistability: near λ_c for finite N there is a hysteretic region. The Wigner function W(α) of the cavity field changes from a Gaussian at origin (normal) to a bimodal distribution (superradiant), shown in phase space.