Long-lived unidirectional flow of active particles within long narrow channels.

Revealing the mechanism of directed transport of active matter is critical for advancing our fundamental understanding of non-equilibrium physics. Asymmetric microstructures are commonly used to rectify random movement of active particles. However, it remains unclear as to how to achieve unidirectional movement of active particles in long narrow channels. Here, we study the dynamics of active particles in a device which is divided into two chambers by V-shaped barriers and connected by a narrow channel. We find three distinct movement modes of active particles within this symmetric channel, including stochastic movement, self-sustained oscillation, and long-lived unidirectional flows. We demonstrate that the three movement modes are determined by the competition between the ratchet effect induced by the V-shaped barriers and the particle transport mediated by the long-narrow channel. Finally, we show that the unidirectional particle flow can serve as an "energy battery" to continuously supply energy for the directed transport of other objects. Our findings offer valuable insights into a unique approach for realizing unidirectional movement of active matter and open new avenues for application in microfluidics and material transport.