Dark-dark-soliton dynamics in two density-coupled Bose-Einstein condensates

作者：Morera I^*; Munoz Mateo A; Polls A; Julia Diaz B

来源：Physical Review A, 2018, 97(4): 043621.

DOI：10.1103/PhysRevA.97.043621

We study the one-dimensional dynamics of dark-dark solitons in the miscible regime of two density-coupled Bose-Einstein condensates having repulsive interparticle interactions within each condensate (g > 0). By using an adiabatic perturbation theory in the parameter g(12)/g, we show that, contrary to the case of two solitons in scalar condensates, the interactions between solitons are attractive when the interparticle interactions between condensates are repulsive g(12) > 0. As a result, the relative motion of dark solitons with equal chemical potential mu is well approximated by harmonic oscillations of angular frequency w(r) = (mu/(h) over bar)root(8/15)g(12)/g. We also show that, in finite systems, the resonance of this anomalous excitation mode with the spin-density mode of lowest energy gives rise to alternating dynamical instability and stability fringes as a function of the perturbative parameter. In the presence of harmonic trapping (with angular frequency Omega) the solitons are driven by the superposition of two harmonic motions at a frequency given by w(2) = (Omega/root 2)(2) + w(r)(2). When g(12) < 0, these two oscillators compete to give rise to an overall effective potential that can be either single well or double well through a pitchfork bifurcation. All our theoretical results are compared with numerical solutions of the Gross-Pitaevskii equation for the dynamics and the Bogoliubov equations for the linear stability. A good agreement is found between them.

• 出版日期2018-4-20