Our modern understanding of quantum mechanical systems, and of many classical systems as well, is founded on particle-wave duality. In essence, this is the idea that physical systems consist of ‘particle’ excitations with well-defined classical attributes like energy, position, and momentum, but that nevertheless interfere with each other like waves. However, in many condensed-matter systems, interactions between particles are strong enough that even the these ‘wavelike’ particles are no longer well-defined, and their place is taken by exotic collective excitations with quantum properties. Our research focuses on understanding the dynamics of these excitations: how they evolve in time, how they can be measured, and especially their interplay with the classical world around, for example when responding to external stimulus.