Abstract:
We report an experimental study of the Wannier-Stark fan and the fractional Wannier-Stark ladder using laser-cooled sodium atoms in an accelerating one-dimensional standing wave of light. We prepare the atoms in the lowest motional band of the optical lattice and then impose a constant acceleration. A weak oscillatory component is added to the acceleration in order to resonantly drive interband transitions, and the number of atoms that remain in the lowest band is measured as a function of the probe frequency. The spectrum is characterized by a ladder of resonances spaced by the atomic Bloch oscillation frequency [Formula Presented] When an additional, strong ac component at frequency [Formula Presented] is added, a fractional ladder is observed with a spacing related to the electric matching ratio [Formula Presented]. © 1999 The American Physical Society.
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