  In this work we demonstrate single microparticle transport in a symmetric
noisy optical ratchet where each potential is a low power ($<2.5$ mW) three
dimensional trap. The optical potentials consist of 20 symmetric optical traps
arranged in a one-dimensional lattice produced by a spatial light modulator.
The external periodic force of the ratchet system adds to zero over one period
(symmetric) and is generated by the motion of a piezo-electric microscope
stage. Transport is achieved by adding noise to the potentials by randomly
varying the diffracted power into the traps at the same frequency of the
external force. We show that the direction and speed of motion (current) is
coupled to the phase difference between the noise in the optical potentials and
the external periodic force.
