  Many unconventional quantum phases host special non-magnetic excitations such
as photons and visons. We discuss two possible ways to detect these excitations
experimentally. Firstly, spin-lattice coupling mixes the excitations with
phonons. The phonon spectral function acquires new features that can be
detected by neutron or X-ray scattering. Secondly, valence-bond fluctuations
translate into charge density fluctuations on non-bipartite lattices. Such
charge fluctuations can be characterized by conventional spectroscopies such as
Terahertz spectroscopy. Observation of exotic singlet excitations would provide
positive identification of unconventional quantum phases in frustrated
antiferromagnets.
