Sub-kHz Rayleigh Resonance in a Cubic Atomic Crystal

We have observed quantized motion of rubidium atoms spatially confined by dipole forces inside microscopic light traps. A cubic lattice of such traps is formed by three mutually orthogonal standing waves. We compare 2D and 3D confinement in the same experiment by observing the absorption of a weak probe laser beam. In both cases we observe Raman transitions between vibrational levels and a central Rayleigh resonance. When we switch to 3D confinement the line width of this Rayleigh resonance dramatically decreases to values below 1 kHz.