Feedback-Controlled Active Brownian Colloids with Space-Dependent Rotational Dynamics

TL;DR

This paper demonstrates how external magnetic fields and feedback control can dynamically tune the rotational diffusion of active colloids, enabling advanced manipulation of their trajectories and behaviors beyond thermal limits.

Contribution

It introduces a novel method to decouple rotational diffusion from thermal noise using magnetic fields and feedback, expanding control over active matter dynamics.

Findings

Achieved tunable rotational diffusivity above and below thermal values.

Observed phenomena like anomalous diffusion, directed transport, and localization.

Enhanced control over active colloid behavior with potential applications in smart materials.

Abstract

The non-thermal nature of self-propelling colloids offers new insights into non-equilibrium physics. The central mathematical model to describe their trajectories is active Brownian motion, where a particle moves with a constant speed, while randomly changing direction due to rotational diffusion. While several feedback strategies exist to achieve position-dependent velocity, the possibility of spatial and temporal control over rotational diffusion, which is inherently dictated by thermal fluctuations, remains untapped. Here, we decouple rotational diffusion from thermal noise. Using external magnetic fields and discrete-time feedback loops, we tune the rotational diffusivity of active colloids above and below its thermal value at will and explore a rich range of phenomena including anomalous diffusion, directed transport, and localization. These findings add a new dimension to the control of active matter, with implications for a broad range of disciplines, from optimal transport to smart materials.