We study the stability of Bose-Einstein condensates with superfluid currents in a one-dimensional periodic potential. By using the Kronig-Penney model, the condensate and Bogoliubov bands are analytically calculated and the stability of condensates in a periodic potential is discussed. The Landau and dynamical instabilities occur in a Kronig-Penney potential when the quasimomentum of the condensate exceeds certain critical values as in a sinusoidal potential. It is found that the onsets of the Landau and dynamical instabilities coincide with the point where the perfect transmission of low energy excitations through each potential barrier is forbidden. The Landau instability is caused by the excitations with small $q$ and the dynamical instability is caused by the excitations with $q=\ensuremath{\pi}∕a$ at their onsets, where $q$ is the quasimomentum of excitation and $a$ is the lattice constant. A swallow-tail energy loop appears at the edge of the first condensate band when the mean-field energy is sufficiently larger than the strength of the periodic potential. We find that the upper portion of the swallow-tail is always dynamically unstable, but the second Bogoliubov band has a phonon spectrum reflecting the positive effective mass.We study the stability of Bose-Einstein condensates with superfluid currents in a one-dimensional periodic potential. By using the Kronig-Penney model, the condensate and Bogoliubov bands are analytically calculated and the stability of condensates in a periodic potential is discussed. The Landau and dynamical instabilities occur in a Kronig-Penney potential when the quasimomentum of the condensate exceeds certain critical values as in a sinusoidal potential. It is found that the onsets of the Landau and dynamical instabilities coincide with the point where the perfect transmission of low energy excitations through each potential barrier is forbidden. The Landau instability is caused by the excitations with small $q$ and the dynamical instability is caused by the excitations with $q=\ensuremath{\pi}∕a$ at their onsets, where $q$ is the quasimomentum of excitation and $a$ is the lattice constant. A swallow-tail energy loop appears at the edge of the first condensate band when the mean-field energy is sufficiently larger than the strength of the periodic potential. We find that the upper portion of the swallow-tail is always dynamically unstable, but the second Bogoliubov band has a phonon spectrum reflecting the positive effective mass.

arXiv:cond-mat/0610582Physical Review AMar 22, 200738 citations

Instabilities and sound speed of a Bose-Einstein condensate in the Kronig-Penney potential

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.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.

Laser PhysicsFeb 1, 200711 citations

Nonlinear dynamics of Bose-Einstein condensates

Chuanwei Zhang

Jan 1, 20050 citations

Modulational Instability in Bose?Einstein Condensates under Feshbach Resonance Management

Zoi Rapti, Georgios Theocharis, P. G. Kevrekidis +2 more

We investigate the modulational instability of nonlinear Schrödinger equations with periodic variation of their coefficients. In particular, we focus on the case of the recently proposed, experimentally realizable protocol of Feshbach Resonance Management for Bose–Einstein condensates. We derive the corresponding linear stability equation analytically and we show that it can be reduced to a Kronig–Penney model, which allows the determination of the windows of instability. The results are tested numerically in the absence, as well as in the presence of the magnetic trapping potential.We investigate the modulational instability of nonlinear Schrödinger equations with periodic variation of their coefficients. In particular, we focus on the case of the recently proposed, experimentally realizable protocol of Feshbach Resonance Management for Bose–Einstein condensates. We derive the corresponding linear stability equation analytically and we show that it can be reduced to a Kronig–Penney model, which allows the determination of the windows of instability. The results are tested numerically in the absence, as well as in the presence of the magnetic trapping potential.

arXiv:cond-mat/0404664Physica ScriptaJan 1, 200420 citations

Stability of Bose-Einstein condensates

博史森瀬

Jan 1, 20030 citations

q

and the dynamical instability is caused by the excitations with $q=\ensuremath{\pi}∕a$ at their onsets, where

q

is the quasimomentum of excitation and

a

is the lattice constant. A swallow-tail energy loop appears at the edge of the first condensate band when the mean-field energy is sufficiently larger than the strength of the periodic potential. We find that the upper portion of the swallow-tail is always dynamically unstable, but the second Bogoliubov band has a phonon spectrum reflecting the positive effective mass.