Observation of atomic Wannier-Stark ladders in an accelerating optical potential.

Atomic Landau-Zener tunneling and Wannier-Stark ladders in optical potentials.

We calculate the quantum motion of ultracold atoms in an accelerating optical potential, and show how they may be used to observe Landau-Zener tunneling and Wannier-Stark ladders, two fundamental quantum effects in solid state physics. The optical potential is spatially periodic, yielding an energy spectrum of Bloch bands for the atoms. The acceleration provides an inertial force in the moving ...

Observation of the Wannier-Stark fan and the fractional ladder in an accelerating optical lattice

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...

Stark-wannier Ladders and Cubic Exponential Sums

Local density of states and level width for Wannier-Stark ladders.

The local density of states ρ(x, E) is calculated for a Bloch electron in an electric field. Depending on the system size, we can see one or more sequences of Wannier-Stark ladders in ρ(x, E), with Lorentz type level widths and apparent spatial localization of the states. Our model is a chain of delta function potential barriers plus a staircase-like electric potential, with open boundary condi...

Coherent delocalization of atomic wave packets in driven lattice potentials.

Atomic wave packets loaded into a phase-modulated vertical optical-lattice potential exhibit a coherent delocalization dynamics arising from intraband transitions among Wannier-Stark levels. Wannier-Stark intraband transitions are here observed by monitoring the in situ wave-packet extent. By varying the modulation frequency, we find resonances at integer multiples of the Bloch frequency. The r...