Magnetic steering of Quincke active rollers for programmable collective states

Systems of active rollers driven by the Quincke electro-rotational instability have been widely utilised to probe emergent collective behavior in active matter. Standard “Quincke'' systems consist of insulating particles which, when in isolation and subject to constant electric driving, exhibit long persistence lengths with no preferred orientation. In these systems, the onset and resultant configuration of cooperative motion rely respectively on two fixed properties---namely the density of particles and the imposed geometric confinement. We introduce a novel approach using magnetite-doped spherical particles to overcome these limitations. Our system combines DC electric field actuation via the Quincke instability, with dynamic magnetic steering using four electromagnets located at the cardinal points. We demonstrate the capacity of our “soft confinement” approach to override fixed geometries by reconfiguring the a priori fixed conformation of the collective state. We also demonstrate the resolution of our collective state steering, to ultimately pave the way for functionalized flocks on-demand and programmable active matter machines.