Fano resonance is a quantum mechanical phenomenon that occurs when a discrete quantum state (such as a bound electron level) interacts with a continuum of states (such as a conduction band or ionization continuum). This interaction causes a unique asymmetric line shape in the absorption or scattering spectrum, which is the hallmark of Fano resonance.
Unlike simple resonances that produce symmetric peaks (like the Lorentzian shape seen in classical systems), Fano resonance appears as a distinctive asymmetric profile—typically a sharp dip followed by a peak. This arises due to the interference between two pathways: one in which a particle transitions directly into the continuum, and another where it first enters the discrete state and then transitions into the continuum. Depending on the relative phase and amplitude of these paths, constructive or destructive interference occurs, shaping the observed resonance.
Fano resonance plays a crucial role in various fields of physics, including atomic physics, nanophotonics, and condensed matter systems. In nanostructures like quantum dots, photonic crystals, and plasmonic nanoparticles, engineers can exploit Fano resonances to design highly sensitive sensors, optical filters, or even quantum information devices.