  Integrating out virtual quantum fluctuations in an originally local quantum
field theory results in an effective theory which is non-local. In this Letter
we argue that tunneling of the 3rd kind - where particles traverse a barrier by
splitting into a pair of virtual particles which recombine only after a finite
distance - provides a direct test of this non-locality. We sketch a
quantum-optical setup to test this effect, and investigate observable effects
in a simple toy model.
