When a coherent matter wave goes through a double slit, it is several layers of excitations (plane waves) of quantum fields?
Fringes are not a wave interfering with the same wave, it is interference with other excitations of different fields?
Mark this day in your calendar as the day the double slit experiment was solved. Decohered waves are compiled to a single wave and do not produce fringes. Coherent waves are many waves from the start.