Dipole rectification in an oscillating electric field

Directed transport of a neutral dimer driven by an ac electric field on a one-dimensional asymmetric substrate is demonstrated. We specialize on the case of a short elastic dimer formed by two bound equal masses carrying opposite charges, i.e. a dipole. The combination of ac drive and binding potential induces a net dipole current (strictly zero for a rigid dimer), which can be optimized by tuning the temperature and the driving frequency with distinct activation energies. Under appropriate operating conditions, a dimer can get rectified more efficiently than its constituents set free, thus implying that particle pairing can actually enhance the ratchet effect.