  We study the transport properties for a walker on a ratchet potential. The
walker consists of two particles coupled by a bistable potential that allow the
interchange of the order of the particles while moving through a
one-dimensional asymmetric periodic ratchet potential. We consider the
stochastic dynamics of the walker on a ratchet with an external periodic
forcing, in the overdamped case. The coupling of the two particles corresponds
to a single effective particle, describing the internal degree of freedom, in a
bistable potential. This double-well potential is subjected to both a periodic
forcing and noise, and therefore is able to provide a realization of the
phenomenon of stochastic resonance. The main result is that there is an optimal
amount of noise where the amplitude of the periodic response of the system is
maximum, a signal of stochastic resonance, and that precisely for this optimal
noise the average velocity of the walker is maximal, implying a strong link
between stochastic resonance and the ratchet effect.
