Displacement phases appear in classical systems

Tony and Eliot (along with Paul Hamilton and Amar Vutha) have published a paper showing how an effect that is typically encountered in quantum systems (the "geometric phase" associated with the displacement operator) can be easily understood by looking at classical systems.  They performed an experiment with classical optics to measure this phase and to help demonstrate its mechanism of action.  The idea is that this paper may help to demystify the appearance of this effect, which often seems surprising to students when they first encounter it.