Asymmetric lineshape from interference between a discrete state and a continuum
The Fano formula σ(E) ∝ (ε+q)²/(1+ε²), where ε=(E−E₀)/(Γ/2). At q=0: pure antiresonance (dark state). q=±∞: symmetric Lorentzian. Intermediate q produces the characteristic asymmetric Fano profile. Ubiquitous in atomic autoionization, Raman spectra, photonic crystals, and plasmonics.