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In a 1996 experiment, ultracold cesium atoms were loaded into the lowest band of an optical standing wave made with $852\mathrm{nm}$ light. Chirping the frequency difference of its counterpropagating beams accelerated the lattice, producing a constant inertial force in its frame. Switching off the lattice after different evolution times allowed momentum-distribution measurements. The observed oscillations tested the periodic band velocity underlying a Bloch oscillation; the lattice period and imposed acceleration controlled the oscillation frequency.^[ref]

In an isolated energy band, semiclassical motion satisfies $\hslash \dot{k}=F$ and $v={\hslash }^{-1}dE/dk$. The band is periodic in crystal momentum, so a constant force sweeps the state through equivalent points of the Brillouin zone. Its velocity repeats rather than increasing without bound. For an electron in a constant electric field, $F=-e\mathcal{E}$, and the Bloch oscillation period isFor $E(k)=E_0-2J\cos ka$, $v=(2Ja/\hslash )\sin ka$ and integration gives a bounded position oscillation of amplitude $2J/|F|$ about its mean. A filled band has no corresponding net transport oscillation after summing uniformly over all $k$.

Observation requires scattering times longer than $T_B$ and negligible interband tunnelling. Ordinary crystals often scatter too rapidly before a full zone traversal; larger-period structures and clean atom-optical lattices help. In the cold-atom Bloch oscillation experiment, accelerating a standing-wave lattice supplied a controlled force, and releasing the atoms at different times revealed an oscillating momentum distribution.^[ref]