  Dispersion interactions such as the van der Waals interaction between atoms
or molecules derive from quantum fluctuations of the electromagnetic field and
can be understood as the exchange of virtual photons between the interacting
partners. Any modification of the environment in which those photons propagate
will thus invariably lead to an alteration of the van der Waals interaction.
Here we show how the two-body dispersion interaction inside a cylindrical
waveguide can be made to decay asymptotically exponentially, and how this
effect sensitively depends on the material properties and the length scales of
the problem, eventually leading to the possibility of controllable
interactions. Further, we discuss the possibility to detect the retarded van
der Waals interaction by resonant enhancement of the interaction between
Rydberg atoms in the light of long-range potentials due to guided modes.
