Southwest Quantum Information and Technology

Directed propagation of cold atoms in a weakly modulated optical lattice – a consequence of simple mechanical resonance or highly selective velocity matching?

Presenting Author: Krishna Pandey, Miami University
Contributing Author(s): : Alexander Staron, Kefeng Jiang, Ian Dilyard, Casey Scoggins, Jordan Churi, Daniel Wingert, Ajitha Dharmasiri, Anthony Rapp, David Cubero, Samir Bali

Atoms confined in a dissipative optical lattice randomly diffuse in all directions, however illumination by a weak probe modulates the lattice leading to directed motion, or ratcheting, of some atoms in a direction perpendicular to the probe propagation. Does this directed ratcheting arise from a mechanical resonance between the probe modulation frequency and the oscillation frequency of the atoms confined in the lattice wells? Or, does it arise from a far more selective velocity matching condition, where the speed at which the probe modulation ripples through the lattice matches the average speed at which the atoms oscillate inside the wells? A probe beam that is propagating along a symmetry axis of the lattice is unable to resolve the issue, because in this case the conditions for mechanical resonance and velocity matching are simultaneously satisfied. We show that a slight misalignment of the probe with respect to the lattice symmetry axis is necessary to create a situation where the condition for velocity matching is satisfied, but not for mechanical resonance. By measuring the probe transmission spectrum we observe that directed propagation still occurs in this situation, proving that velocity matching is the origin for this form of cold atom ratchet. The spectral signature for unidirectional propagation is investigated as a function of off-axis angle and lattice well-depth. The data are found to agree well with theory, using no fitting parameters.

(Session 5 : Thursday from 5:00 pm - 7:00 pm)