  Understanding inter-site mutual mode interaction in coupled physical systems
is essential to comprehend large compound systems as this local interaction
determines the successive multiple inter-site energy transfer efficiency. We
demonstrate that only the non-Hermitian coupling can correctly account for the
light transfer between two coupled optical cavities. We also reveal that the
non-Hermitian coupling effect becomes much crucial as the system dimension gets
smaller. Our results provide an important insight to deal with general
coupled-devices in the quantum regime.
