Abstract
Two thin films separated by a tunnel barrier represent two coupled electron systems. The decay of quantum interference and its contribution to the conductance is calculated. The finite coherence time acts as an imaginary energy. The systems can be decoupled mathematically, resulting in new quasifilms (similar to the diagonalizatoin for coupled energy states). Such a system can be investigated experimentally by magnetoresistance measurements (weak localization) and permits the study of a tunneling junction with very small tunneling resistance. No voltage has to be applied across the tunneling junction.