  We study ensembles of Rydberg atoms in a confined electromagnetic environment
such as provided by a microwave cavity. The competition between standard free
space Ising type and cavity-mediated interactions leads to the emergence of
different regimes where the particle-particle couplings range from the typical
van der Waals $r^{-6}$ behavior to $r^{-3}$ and to $r$-independence. We apply a
Ramsey spectroscopic technique to map the two-body interactions into a
characteristic signal such as intensity and contrast decay curves. As opposed
to previous treatments requiring high-densities for considerable contrast and
phase decay, the cavity scenario can exhibit similar behavior at much lower
densities.
