  The "spin ice" state found in the rare earth pyrochlore magnets Ho2Ti2O7 and
Dy2Ti2O7 offers a beautiful realisation of classical magnetostatics, complete
with magnetic monopole excitations. It has been suggested that in "quantum spin
ice" materials, quantum-mechanical tunnelling between different ice
configurations could convert the magnetostatics of spin ice into a quantum spin
liquid which realises a fully dynamical, lattice-analogue of quantum
electromagnetism. Here we explore how such a state might manifest itself in
experiment, within the minimal microscopic model of a such a quantum spin ice.
We develop a lattice field theory for this model, and use this to make explicit
predictions for the dynamical structure factor which would be observed in
neutron scattering experiments on a quantum spin ice. We find that "pinch
points", seen in quasi-elastic scattering, which are the signal feature of a
classical spin ice, fade away as a quantum ice is cooled to its
zero-temperature ground state. We also make explicit predictions for the
ghostly, linearly dispersing magnetic excitations which are the "photons" of
this emergent electromagnetism. The predictions of this field theory are shown
to be in quantitative agreement with Quantum Monte Carlo simulations at zero
temperature.
