Optical Traps for Neutral Atoms

Abstract

The force on atoms confined in the magnetic traps described in Chapter 10 arises from the permanent magnetic dipole moments of the atoms in the inhomogeneous field of the trap. By contrast, the inversion symmetry of atomic wave functions prevents them from having permanent electric dipole moments, so optical trapping of neutral atoms by electrical interaction must proceed by inducing a dipole moment. This can be accomplished either by electrostatic fields or by nearly resonant optical frequency fields. Inducing appropriate dipole moments with dc fields can be accomplished in atoms that have a sufficiently close-lying energy states of opposite parity (this excludes most atomic ground states but favors Rydberg states). By contrast, there are several types of optical traps that employ various configurations of laser beams [40, 41]. These produce not only the mixing of atomic states of opposite parity needed to provide dipole moments for interaction with the field, but also the strong field gradients appropriately arranged for such trapping.