  Light-matter coupling strength and optical loss are two key physical
quantities in cavity quantum electrodynamics (cQED), and their interplay
determines whether light-matter hybrid states can be formed or not in chemical
systems. In this study, by using macroscopic quantum electrodynamics (mQED)
combined with a pseudomode approach, we present a simple but accurate method
which allows us to quickly estimate the light-matter coupling strength and
optical loss without free parameters. Moreover, for a molecular emitter coupled
with photonic modes (including cavity modes and plasmon polartion modes), we
analytically and numerically prove that the dynamics derived from the
mQED-based wavefunction approach is mathematically equivalent to the dynamics
governed by the cQED-based Lindblad master equation when the Purcell factor
behaves like Lorentzians.
