Figure 2: Atomic dispersion in lattice.
From: Veselago lensing with ultracold atoms in an optical lattice
The figure shows the dispersion relation of rubidium atoms in the bichromatic optical lattice for V1=2.1Er, V2=0.28Er and a relative phase between lattice harmonics of ϕ=180° (solid) and ϕ=0° (dashed). In the former case, the splitting between the first (red solid line) and the second (blue solid line) excited Bloch band vanishes and the dispersion near the crossing becomes linear, that is, relativistic. The zero of the energy scale is here set to the position of the crossing. Transitions between the branch of the dispersion relation with E>0, corresponding to the case with collinear wavevector and group velocity, and the regime with E<0, for which wavevector and group velocity are antiparallel, can be induced by four-photon Raman π-pulses.
