  We study a new kind of tunneling of particles through a barrier particular to
quantum field theory. Here, the particles traverse the barrier by splitting
into a virtual pair of particles of a different species which interacts only
very weakly with the barrier and can therefore pass through it. Behind the
barrier, the pair recombines into a particle of the original species. As an
example, we discuss the case where photons split into a pair of minicharged
particles. This process could be observed in experiments of the
light-shining-through-a-wall type and may be used to search for minicharged
particles in laboratory experiments.
