We analyze the energetic and dynamical properties of bright-bright (BB) soliton pairs in a binary mixture of Bose-Einstein condensates subjected to the action of a combined optical lattice, acting as an external potential for the first species while modulating the intraspecies coupling constant of the second. In particular, we use a variational approach and direct numerical integrations to investigate the existence and stability of bright-bright (BB) solitons in which the two species are either spatially separated (split soliton) or located at the same optical lattice site (overlapped soliton). The dependence of these solitons on the interspecies interaction parameter is explicitly investigated. For repulsive interspecies interaction we show the existence of a series of critical values at which transitions from an initially overlapped soliton to split solitons occur. For attractive interspecies interaction only single direct transitions from split to overlapped BB solitons are found. The possibility to use split solitons for indirect measurements of scattering lengths is also suggested.
We analyze the energetic and dynamical properties of bright-bright (BB) soliton pairs in a binary mixture of Bose-Einstein condensates subjected to the action of a combined optical lattice, acting as an external potential for the first species while modulating the intraspecies coupling constant of the second. In particular, we use a variational approach and direct numerical integrations to investigate the existence and stability of bright-bright (BB) solitons in which the two species are either spatially separated (split soliton) or located at the same optical lattice site (overlapped soliton). The dependence of these solitons on the interspecies interaction parameter is explicitly investigated. For repulsive interspecies interaction we show the existence of a series of critical values at which transitions from an initially overlapped soliton to split solitons occur. For attractive interspecies interaction only single direct transitions from split to overlapped BB solitons are found. The possibility to use split solitons for indirect measurements of scattering lengths is also suggested.
Abstract By using the Crank–Nicolson method, we investigate numerically the dynamical properties of bright–bright solitons in two species Bose–Einstein condensates (BECs) trapped in an optical lattice. We confirm that the soliton splitting behavior occurs at a critical depth of optical potential. The splitting behavior of solitons and the fusion behavior of condensates can be accurately controlled by adjusting the depth and lattice parameter of optical potential, the initial amplitude and position of solitons, and the interspecies interactions. When the lattice parameter is fixed but the interspecies interaction increased exponentially with the time, each soliton splits into two soltions with different amplitude, and partial fusion of two species BECs can be found. While the interspecies interaction remains unchanged but the lattice parameter increases exponentially with the time, interestingly, the bright solitons with zero initial velocity can pass through each other and accomplish a transmission collision. Furthermore, for the case of both the interspecies interaction and lattice parameter increased exponentially with the time, a head-on collision of the bright solitons in two species BECs occurred. After the collision, each soliton splits into two soltions with equal amplitude. Meanwhile, the complete fusion of two species BECs can be observed. The relevant results can provide help for the precise manipulation of BECs experiments.
Considering repulsive interspecies interactions, we study the dynamical properties of bright-bright solitons in two species Bose—Einstein condensates by using a variational approach combined with numerical simulation. It is shown that the interactions between bright-bright solitons vary from repulsive to attractive interactions with the increasing their separating distances, and at equilibrium position the bright-bright solitons are localized. Interestingly, a transition from reflection- to transmission-collision is firstly observed, different from previous results of only reflection collision appearing there. These results will be helpful for the experimental manipulating such solitons.
We consider effects of interspecies attraction on two-component gap solitons (GSs) in the binary BEC with intraspecies repulsion, trapped in the one-dimensional optical lattice (OL). Systematic simulations of the coupled Gross-Pitaevskii equations corroborate an assumption that, because the effective mass of GSs is negative, the interspecies attraction may split the two-component soliton. Two critical values, ${\ensuremath{\kappa}}_{1}$ and ${\ensuremath{\kappa}}_{2}$, of the OL strength $(\ensuremath{\kappa})$ are identified. Two-species GSs with fully overlapping wave functions are stable in strong lattices $(\ensuremath{\kappa}>{\ensuremath{\kappa}}_{1})$. In an intermediate region, ${\ensuremath{\kappa}}_{1}>\ensuremath{\kappa}>{\ensuremath{\kappa}}_{2}$, the soliton splits into a double-humped state with separated components. Finally, in weak lattices $(\ensuremath{\kappa}<{\ensuremath{\kappa}}_{2})$, the splitting generates a pair of freely moving single-species GSs. We present and explain the dependence of ${\ensuremath{\kappa}}_{1}$ and ${\ensuremath{\kappa}}_{2}$ on the number of atoms (total norm), and on the relative strength of the competing interspecies attraction and intraspecies repulsion. The splitting of asymmetric solitons, with unequal norms of the two species, is briefly considered too. It is found and explained that the splitting threshold grows with the increase of the asymmetry.
Using the variational approximation and numerical simulations, we study one-dimensional gap solitons in a binary Bose-Einstein condensate trapped in an optical-lattice potential. We consider the case of interspecies repulsion, while the intraspecies interaction may be either repulsive or attractive. Several types of gap solitons are found: symmetric or asymmetric; unsplit or split, if centers of the components coincide or separate; intragap (with both chemical potentials falling into a single band gap) or intergap, otherwise. In the case of the intraspecies attraction, a smooth transition takes place between solitons in the semi-infinite gap, those in the first finite band gap, and semigap solitons (with one component in a band gap and the other in the semi-infinite gap).
The characteristics of two coupled Bose-Einstein Condensate (BEC) bright solitons trapped in an optical lattice are investigated with the variational approach and direct numerical simulations of the Gross-Pitaevskii equation. It is found that the optical lattice can be controllably used to capture and drag the coupled BEC solitons. Its effect depends on the initial location of the BEC solitons, the lattice amplitude and wave-number, and the amplitude of the coupled BEC solitons. The effective interaction between the two coupled solitons is the attractive effect.
Considering the time-dependent interspecies interactions, we study the dynamic behaviors of bright-bright solitons in two species Bose-Einstein condensates in the harmonic external potentials. In the presence of unchanged attractive interspecies and intraspecies interactions, bright-bright solitons exhibit periodic oscillations. When the attractive intraspecies interactions are fixed but the attractive interspecies interactions are increased exponentially, interestingly, a transition behavior from oscillation to localization is observed. Meanwhile, this transition behavior can be controlled by tuning the transverse trapping frequency of harmonic potential. Furthermore, an experimental protocol is designed to observe the transition behavior in the current experimental conditions.