  Interatomic Coulombic decay (ICD) is a mechanism which allows microscopic
objects to rapidly exchange energy. When the two objects are distant, the
energy transfer between the donor and acceptor species takes place via the
exchange of a virtual photon. On the contrary, recent ab initio calculations
have revealed that the presence of a third passive species can significantly
enhance the ICD rate at short distances due to the effects of electronic wave
function overlap and charge transfer states [Phys. Rev. Lett. 119, 083403
(2017)]. Here, we develop a virtual photon description of three-body ICD,
showing that a mediator atom can have a significant influence at much larger
distances. In this regime, this impact is due to the scattering of virtual
photons off the mediator, allowing for simple analytical results and being
manifest in a distinct geometry-dependence which includes interference effects.
As a striking example, we show that in the retarded regime ICD can be
substantially enhanced or suppressed depending on the position of the
ICD-inactive object, even if the latter is far from both donor and acceptor
species.
