The exponential divergence of quasinormal modes: physical or unphysical?

Nanoresonators enhance many light-matter-interaction processes and are used in various modern applications in nano-quantum optics. They are open systems and their eigenstates are always leaky and have a finite lifetime (complex frequency), even when they are dark states. The consequence of the leakage is that the modal field exponentially growths outside the resonators. This growth is often seen as unphysical. We challenge this opinion.