A particle of energy E tunnels through two rectangular barriers. Transfer matrix gives exact transmission T(E). At resonant energies (quasi-bound states in well), T=1: perfect transmission! The dwell time τ_d = dφ/dE diverges at resonance — Eisenbud-Wigner-Smith effect.
Transmission T(E): — | Reflection R: — | Phase velocity delay | Hartman effect: τ independent of barrier width