Ponderomotive Optical Lattice Trap for Rydberg Atoms
Georg Raithel lab, University of Michigan
Participating Students: Yun-Jhih Chen, Kaitlin Moore, Andira Ramos
(Illustration credit: Kelly Younge)
Ponderomotive Optical Lattice
The trapping mechanism for a Rydberg atom in an optical lattice exploits the fact that the Rydberg electron is so loosely bound that it can be considered quasi-free. The oscillating electric field of the lattice standing wave creates a ponderomotive potential that traps the quasi-free electron at a lattice intensity minimum. The entire atom is then trapped due to the Coulomb force binding the core of the atom to the electron. Further details on the trapping mechanism for Rydberg atoms in an optical lattice can be found at Phys. Rev. Rev. 85, 5551 (2000).
Compared to ground-state optical lattices, a novel feature exhibited by this system arises from the large size of the Rydberg atom, which can be on the order of the width of the lattice potential well (~0.5 um in our setup). The large spatial extent of the Rydberg atom causes it to experience a unique state-dependent trapping potential in the lattice. Technically speaking, the potential that a Rydberg atom experiences in the lattice is a spatial average of the free electron ponderomotive potential weighted by the Rydberg wavefunction. The figure below illustrates the state-dependence of the trapping potential. In general, the larger Rydberg atom (blue) can average over more of the free electron ponderomotive potential (dashed) than the smaller Rydberg atom (green), leading to a shallower potential.
Since the potentials that Rydberg atoms experience in the lattice are determined by the overlap of the Rydberg wavefunction and the lattice intensity, the Rydberg-trapping potentials therefore depend on the shapes of the Rydberg wavefunctions and their orientation with respect to the lattice planes. This unique aspect of Rydberg-atom optical lattices can be used to tailor the lattice potential as needed for applications.
A cloud of atoms from our magneto-optical trap distorted into the shape of a Michigan 'M'.