  Optical phenomena associated with extremely localized field often should be
understood with the consideration of nonlocal and quantum effects, which pose a
difficult hurdle to conceptualize the physics with a few governing modes. Here
we first propose a generalized Lorentz model to describe these effects and then
develop a procedure to calculate and orthonormalize the quasinormal modes
(QNMs) of the system, establishing a general canonical QNM theory for extreme
nano-optics. Concrete formulism for materials described by the quantum
hydrodynamic model is provided. The theory enables for the first time analyzing
optical responses in quantum tunneling regime with quasinormal modes.
