  We consider the effect of adding quantum dynamics to a classical topological
spin liquid, with particular view to how best to detect its presence in
experiment. For the Coulomb phase of spin ice, we find quantum effects to be
most visible in the gauge-charged monopole excitations. In the presence of weak
dilution with nonmagnetic ions we find a particularly crisp phenomenon, namely
the emergence of hydrogenic excited states in which a magnetic monopole is
bound to a vacancy at various distances. Via a mapping to an analytically
tractable single particle problem on the Bethe lattice, we obtain an
approximate expression for the dynamic neutron scattering structure factor.
