Enhancement of the irreversibility of active processes in viscoelastic bath

Non-equilibrium active processes are mostly discussed assuming a clear separation of timescales between the system and environment that eventually leads to an effective Markovian description. However, such assumptions will break down if the environment is viscoelastic as the relaxation time of the fluid will be comparatively higher than the viscous media. The effects of viscoelasticity in shaping different active processes are relatively less explored. In this work, with a minimal experiment using a driven colloid in viscous and viscoelastic baths, we show that viscoelasticity significantly increases the mean injected power to the passive object (∼ 50% compared to a viscous medium), for the same strength of the external driving. Additionally, we observe a notable reduction in negative work fluctuations across a wide range of driving amplitudes. These findings along with an increased rate of entropy production suggest an enhanced irreversibility in driven processes within a viscoelastic bath, which we attribute to the emergence of interactions between the colloid and the viscoelastic medium. We provide a Langevin-based model from which exact analytical results corresponding to the dynamics and fluctuations of the work done in the process are deduced using novel techniques to corroborate all our experimental and numerical findings.