Mesoscopic stochastic systems at equilibrium are constrained by detailed balance and cannot sustain directed motion or perform work. It is only when they are driven out of equilibrium that they acquire the ability to act: transducing energy, generating forces, and exhibiting nontrivial responses.

In this talk, I present two experimental approaches to induce and exploit such nonequilibrium behavior in interacting many-body systems across micro- and macroscopic scales.

The first implements a Maxwell demon: by measuring the fluctuating state of a colloidal suspension and applying feedback, the system is driven out of equilibrium. This enables an information engine that extracts work from a single heat bath and transfers it to a probe particle.

The second system is a chiral active fluid composed of self-propelled macroscopic bristle-bots. Here, nonequilibrium arises from sustained energy injection at the level of individual propulsion. Because of the fluid’s chirality, a probe particle embedded in this medium exhibits an odd response to external forces, beyond the standard rheology of complex fluids.