Origin of directed atomic propagation in driven dissipative optical lattices: Prospects for precisely controlled ratcheting with quasiperiodic driving fields

Atoms confined in a three-dimensional dissipative optical lattice oscillate inside potential wells, and occasionally hop to adjacent wells, thereby diffusing in all directions. Illumination by a weak probe beam modulates the lattice, yielding propagating atomic density waves that travel perpendicular to the direction of travel of the probe. Experimental and theoretical investigations have revealed that if the probe propagates along a lattice symmetry axis, this directed motion of the atoms originates from a resonance between the intrawell atomic oscillation frequency and the modulation frequency. On the other hand, if the probe does not propagate along the symmetry axis, this results in a spatial quasiperiodic driving of the lattice. In this case, the propagating atomic density modes originate from a velocity matching between the atomic density wave and a propagating modulation wave created by the off-axis probe. Further exploration of quasiperiodic driving, for example in the time domain, may yield directed atomic propagation in highly controlled, arbitrary directions.