Energy recuperation of driven colloids in non-Markovian baths.

When objects move through a classical fluid, their motion is primarily governed by viscous friction, which is irreversibly converted into heat. At microscopic scales, this energy dissipation presents challenges for applications, such as microscopic heat engines and microrobots relying on externally driven or self-propelled colloidal particles. In this study, we experimentally demonstrate energy recuperation (ER) in a colloidal particle driven through a viscoelastic fluid, recovering up to 30% of the energy injected into the surrounding medium as useful work. This effect, which significantly reduces the friction experienced by the particle, arises from the time-delayed response of the bath to external forces, preventing immediate relaxation to equilibrium. As a result, energy is temporarily stored, enabling bidirectional energy exchange between the non-equilibrium bath and the particle. Our experimental results are in excellent agreement with a micro-mechanical model that captures this delayed response, suggesting that similar energy recovery mechanisms could be applicable to a broad range of non-Markovian environments, including critical fluids and active baths.