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

Abstract

We study the 1D 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 g12/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 g12 > 0. As a result, the relative motion of dark solitons with equal chemical potential µ is well approximated by harmonic oscillations of angular frequency wr = (µ/ ) (8/15)g12/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 Ω) the solitons are driven by the superposition of two harmonic motions at a frequency given by w 2 = (Ω/ √ 2) 2 + w 2 r . When g12 < 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. arXiv:1801.00309v1 [cond-mat.quant-gas]

Nondegenerate bound-state solitons in multicomponent Bose-Einstein condensates

“…The dark soliton state is a free state, and it admits a wide non-zero density background. This character is admitted by most of previous vector solitons in BECs systems [4][5][6][7][8][9]. We would like to look for nondegenerate bound state solitons (NDBSSs), for which all eigen-states are bound states.…”

“…The multi-component coupled Bose-Einstein condensates (BECs) provide a good platform to study the dynamics of vector solitons [1]. Many different vector solitons have been obtained in the two-component coupled BEC systems, such as the bright-bright soliton [2,3], the bright-dark soliton [4], the dark-antidark soliton [5], the dark-dark soliton [6,7], and the dark-bright soliton [8,9]. The soliton states can be related with eigen-states in quantum well [10,11].…”

On-demand generation of dark soliton trains in Bose-Einstein condensates

“…The experimental realization of two-component BECs [7][8][9] has opened a window towards the study of more complex solitonic structures [10][11][12][13][14][15][16][17][18][19]. In repulsive two-component BECs, a fundamental excitation takes the form of a dark-bright (DB) soliton [10].…”

“…The first experimental realizations of DB solitons in BECs almost a decade ago [14,[27][28][29][30][31], as well as subsequent experimental realizations of their variants and generalizations [15,19,[32][33][34][35] have motivated a significant amount of interest in studying their dynamics and interactions [18,[36][37][38][39][40][41][42][43][44][45][46][47]. In particular, several methods have been proposed to create DB soliton structures.…”

Bound states of dark solitons and vortices in trapped multidimensional Bose-Einstein condensates

“…confinement) balances the repulsive interaction between them [23]. Interestingly, it has been recently reported that in systems with two overlapped BECs the intersoliton forces can show either repulsive or attractive character depending on the sign of the interatomic interactions between condensates [29].…”