Emergent activity arises from wave scattering

Active matter, a form of matter with components that consume energy and convert it to motion, has already spurred the discovery of new materials properties. Thus far, active matter has been limited to systems with individually driven components. A different form of activity can arise when passive particles exhibit nonreciprocal interactions. While individual particles remain stationary, clusters of particles gain the ability to transduce energy from the environment and use it to propel their motion. These systems exhibit emergent activity, which arises only as a collective property of the system’s state of organization. In this talk, I will demonstrate that passive particles immersed in a wave have generically nonreciprocal interactions, and that these interactions drive emergent activity in optically and acoustically levitated particles. This work therefore creates a bridge between the fields of active matter and wave mechanics.