Optimal control of active nematics in bulk and confined geometries.

Being intrinsically nonequilibrium, active materials have control to perform functions that would be thermodynamically forbidden in passive materials. However, active systems

exhibit diverse local attractors that correspond to distinct dynamical states, many of which exhibit chaotic turbulent-like dynamics. Designing such a system to choose a specific dynamical state to perform a desired function is a formidable challenge. Motivated by recent advances enabling optogenetic control of experimental active materials, we have used optimal control theory to identify spatiotemporal sequences of light-generated activity that direct the dynamics of active matter towards a predetermined steady-state. In this presentation, we will focus on applying this approach to 2D active nematics, which exhibit spontaneous defect proliferation and chaotic streaming dynamics in the absence of control. We find that optimal control theory identifies time-varying active stress fields that guide the system to a variety of dynamical states and functional programs. These include selecting and stabilizing spatiotemporal behaviors that are unstable in the uncontrolled system, and dynamically reconfiguring between dynamical states. Our results lay out a roadmap to leverage optimal control methods to design structure, dynamics, and function in a wide variety of active materials.