  Virtual photons play an essential role in the locally realistic description
of the Aharonov-Bohm interference. We show that the effect of virtual photons
in the interferometer is manifested by a change in their spectrum. In
particular, when a vacuum is confined between two ideal conducting plates, the
photons obey the two-dimensional Proca equation, the wave equation with finite
effective mass. This results in a short-range interaction between a test charge
and a magnetic flux, and hence the Aharonov-Bohm effect is reduced
exponentially at a large distance between the two bodies. On the other hand, a
semiclassical description is also possible, and this raises the interesting
question of how to prove the physical reality of virtual photons.
