2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/214307Feedback flashing ratchets are thermal rectifiers that use information on the state of the system to operate the switching on and off a periodic potential. We discuss different strategies for this operation with the aim of maximizing the net flux of particles in the collective version of a flashing ratchet consisting on N overdamped Brownian particles. We show the optimal protocols for the one-particle ratchet and for the collective ratchet with an infinite number of particles. Finally we comment on the unsolved problem of the optimal strategy for any other number of particles.LaTeX, 5 pages, 2 figures. Presented at the 5th International Conference on Unsolved Problems on Noise (UPON'08). Selected to appear in Journal of Statistical Mechanics (JSTAT)Statistical Mechanicstext