  This paper investigates the Fano-Feshbach resonance with a two-channel
coupled-square-well model in both the frequency and time domains. This systems
is shown to exhibit Fano lineshape profiles in the energy absorption spectrum.
The associated time-dependent dipole response has a phase shift that has
recently been understood to be related to the Fano lineshape asymmetric $q$
parameter by $\phi=2arg(q-i)$. The present study demonstrates that the
phase-$q$ correspondence is general for any Fano resonance in the weak coupling
regime, independent of the transition mechanism.
