Stability Diagrams of a Bose-Einstein Condensate in Excited Bloch Bands

Hiroki Saito

Tobias Klafka, Alexander Ilin, Julius Seeger +3 more

Liang Zhao-Xin, Hu Ban-Bi

Landau and dynamical instabilities of a Bose–Einstein condensate (BEC) in the excited bands of a one-dimensional optical lattice are investigated by the Gross–Pitaevskii theory. Our results show that there always exists Landau instability for a BEC in the whole region of excited bands. We also map out the dangerous zones of the dynamical instability. The experimental implications of the stability diagram are discussed.

Xi Dong, Biao Wu

We analyze the full set of Bloch wave stationary solutions for a Bose-Einstein condensate in the Kronig-Penney potential. We investigate the Landau instability and dynamical instability of the Bloch states in the lowest Bloch band, including the loop if it appears. The stability phase diagrams are shown to be similar as in the case of the sinusoidal optical lattice potential. We also compute the speed of sound as a function of the potential strength. The trend is shown to be similar to the sinusoidal case, reflecting our general conclusion that, in any one-dimensional periodic potential, the sound speed always falls monotonically with increasing potential strength, no matter whether the atomic interaction is weak or strong. The Kronig-Penney potential, being analytically tractable and hence more advantageous than the sinusoidal potential, therefore serves as a good model for understanding the phenomena of Bose-Einstein condensation.

Jian Zhang

Dirk Witthaut, F. Trimborn, V. Kegel +1 more

We study the dynamics of Bose-Einstein condensates in tilted and driven optical superlattices. For a bichromatic lattice, each Bloch band splits up into two minibands such that the dynamics is governed by the interplay of Bloch oscillations and transitions between the bands. Thus, bichromatic potentials provide an excellent model system for the study of nonlinear Landau-Zener tunneling, and they allow for a variety of applications in matter-wave interferometry and quantum metrology. In the present paper, we investigate the coherent dynamics of an interacting Bose-Einstein condensate as well as its stability. Different mechanisms of instability are discussed, which lead to a rapid depletion of the condensate.