Does electromagnetic field collapse the wave function of charged particles? In an electron double slit experiment, let's put two charged plates behind the slits in an attempt to move the pattern up and down on the the screen.
What will happen? Will it just shift the interference pattern on the screen or washes it out completely? 
If it washes it out, what's the minimal field that doesn't affect the pattern? Since I don't believe the electron double slit experiment was performed in an environment where all fields were exactly zero, but they still managed to get the pattern.
 A: If we can neglect the internal modes of the charged plates, they merely modify the potential in which electrons propagate, i.e., the potential of the slits. Depending on configuration it may change the interference pattern, but it does not destroy the interference.
On the other hand, if the plates have their own modes, they may cause dephasing and/or decoherence and destroy the interference. This is also the case, if electrons are coupled to electromagnetic field and can lose/absorb energy or simply be scattered by photons.
It is necessary to note that the double slit experiment is a thought experiment - although it has been realized literally, the relevant phenomena can be studied in many physical situations and configurations. E.g., the destruction of the interference picture has been extensively analyzed in solid-state Aharonov-Bohm interferometers.
A: https://commons.m.wikimedia.org/wiki/File:Moellenstedt_biprisma_voltage_shadow.JPG
It shows the influence of an electrical field to fringes.
https://commons.m.wikimedia.org/wiki/File:Moellenstedt_biprisma_schematic_arrangement.JPG
This shows how experiment with electrons was arranged in generally.
As a result you may find out that the potential of the material which forms the slits is responsible for changes in fringes dimensions. Ergo can we say that the potential is responsible for the fringes at all?
