Active fluctuations drive inertia-free absolute negative mobility in soft and living matter

Absolute negative mobility (ANM) is one of the most paradoxical transport phenomena in which a setup moves on average in a direction opposite to the applied force. The simplest system exhibiting this effect in minimal one-dimensional dynamics involves an inertial particle subjected to a constant bias while dwelling in a nonlinear, symmetric periodic potential in a nonequilibrium, nonstationary state generated by external driving. The necessity of inertia poses a significant conceptual barrier in predicting the ANM in a microscopic world of soft and living matter such as biological cells. In this work, we solve a two-decade old puzzle and demonstrate that none of the previously thought factors required for this effect are decisive. We show that the ANM may occur in a system composed of an overdamped particle in a piecewise linear symmetric periodic potential in an equilibrium state, provided that it is additionally driven by active fluctuations in the form of white Poisson shot noise. Our result may help to explain exotic transport behavior emerging in biological cells where dynamics is typically overdamped and assisted by active fluctuations derived from various metabolic activities. It can also be exploited for effective separation strategies in a microscopic world, thus transforming fluctuations from a nuisance into a functional resource.