Noise-Enabled Optical Ratchets

In this work we demonstrate single microparticle transport enabled by noise in a one dimensional optical lattice with periodic symmetric potentials and a small constant external force. The one dimensional lattice is implemented by six focused beams with holographic optical tweezers, where a microparticle is trapped in three dimensions. Transport initiates when dynamical disorder is added to the diffracted laser power at each trap ($\pm 30\%$) at a fixed frequency (0 to 35 Hz), while the direction of motion is set by the constant external force. We find that transport is only achieved within a narrow noise frequency range, which is consistent with simulations, and the predicted behavior and observations of noise-induced energy transport in quantum and classical systems. To our knowledge this is the first direct observation of noise-assisted transport in a colloidal system.