Counterintuitive Short Uphill Transitions in Single-File Diffusion

A universal feature of single-file transport in micropores is the anomalous diffusion of a tracer particle. Here, we report on a new inherent property of the tracer dynamics in periodic free energy landscapes, which manifests itself in the kinetics of local transitions between neighboring energy minima: in the presence of a drift, transitions uphill against the drift are faster than along the more favorable downhill direction. The inequality between the uphill and downhill transition times holds for all densities and particle sizes. Dependent on the particle size, the transition times can be shorter or longer than the corresponding ones for a single particle. We provide a clear physical interpretation of these behaviors and show how they appear in various regimes of collective dynamics. Our findings provide a new robust method to probe collective effects by measurements of local tracer dynamics. They moreover demonstrate the complexity of extending Kramers' diffusion model to an interacting many-body system.