First passage of an active particle in the presence of passive crowders

Abstract

We experimentally study the stochastic transport of a self-propelled camphor boat, driven by Marangoni forces, through a crowd of passive paper discs floating on water. We analyze the statistics of the first passage times of the active particle to travel from the center of a circular container to its boundary. While the mean times rise monotonically as a function of the covered area fraction ϕ of the passive paper discs, their fluctuations show a non-monotonic behavior – being higher at low and high value of ϕ compared to intermediate values. The reason is traced to an interplay of two distinct sources of fluctuations – one intrinsic to the dynamics, while the other due to the crowding.