  Thanks to a constant energy input, active matter can self-assemble into
phases with complex architectures and functionalities such as living clusters
that dynamically form, reshape and break-up, which are forbidden in equilibrium
materials by the entropy maximization (or free energy minimization) principle.
The challenge to control this active self-assembly has evoked widespread
efforts typically hinging on engineering of the properties of individual motile
constituents. Here, we provide a different route, where activity occurs as an
emergent phenomenon only when individual building blocks bind together in a way
that we control by laser light. Using experiments and simulations of two
species of immotile microspheres, we exemplify this route by creating active
molecules featuring a complex array of behaviors, becoming migrators, spinners
and rotators. The possibility to control the dynamics of active self-assembly
via light-controllable nonreciprocal interactions will inspire new approaches
to understand living matter and to design active materials.
