  The elementary excitations of a state of matter consisting of large
collection of interacting particles can be very different from the original
particles. In the most interesting examples, the particles effectively
decompose into smaller constituent particles, which only carry a fraction of
their quantum numbers. When these constituents are free, as in fractionally
quantised Hall states, it is conceptually clear how to observe them. But what
if they are confined, as it might be the case in spin liquids hypothesised to
describe high Tc superconductors?
