Formation of combined solitons in two-component Bose—Einstein condensates

We investigate the combined soliton solutions of two-component Bose-Einstein condensates with external potential. The ＂phase diagram＂ is obtained for the formation regions of different combined solitons. Our results show that the intraspecies （interspecies） interaction strengths and the external trapped potential clearly affect the formation of dark- dark, bright-bright, and dark bright soliton solutions in different regions. Especially, we find that the bright bright （dark^dark） soliton can exist in the case of both repulsive （attractive） intraspecies interaction strengths in the presence of external potential. This novel phenomenon is completely different from the formation of soliton solution of one- component Bose-Einstein condensates without external potential, and it will be useful for the study of two-component Bose-Einstein condensates.

Effect of interaction strength on gap solitons of Bose-Einstein condensates in optical lattices

We have developed a systematic analytical approach to the study on the dynamic properties of the linear and the nonlinear excitations for quasi-one-dimensional Bose-Einstein condensate trapped in optical lattices. A novel linear dispersion relation and an algebraic soliton solution of the condensate are derived analytically under consideration of Bose-Einstein condensate with a periodic potential. By analysing the soliton solution, we find that the interatomic interaction strength has an important effect on soliton dynamic properties of Bose-Einstein condensate.

Dynamic stability and manipulation of bright matter-wave solitons by optical lattices in Bose-Einstein condensates

An extended variation approach to describing the dynamic evolution of self-attractive Bose-Einstein condensates is developed. We consider bright matter-wave solitons in the presence of a parabolic magnetic potential and a timespace periodic optical lattice. The dynamics of condensates is shown to be well approximated by four coupled nonlinear differential equations. A noteworthy feature is that the extended variation approach gives a critical strength ratio to support multiple stable lattice sites for the condensate. We further examine the existence of the solitons and their stabilities at the multiple stable lattice sites. In this case, the analytical predictions of Bose-Einstein condensates variational dynamics are found to be in good agreement with numerical simulations. We then find a stable region for successful manipulating matter-wave solitons without collapse, which are dragged from an initial stationary to a prescribed position by a moving periodic optical lattice.

Feshbach resonance management of vector solitons in two-component Bose-Einstein condensates

We consider two coupled Gross Pitaevskii equations describing a two-component Bose Einstein condensate with time-dependent atomic interactions loaded in an external harmonic potential, and investigate the dynamics of vector solitons. By using a direct method, we construct a novel family of vector soliton solutions, which are the linear combination between dark and bright solitons in each component. Our results show that due to the superposition between dark and bright solitons, such vector solitons possess many novel and interesting properties. The dynamics of vector solitons can be controlled by the Feshbach resonance technique, and the vector solitons can keep the dynamic stability against the variation of the scattering length.

Moving Matter-Wave Solitons in Spin-Orbit Coupled Bose-Einstein Condensates

We investigate the moving matter-wave solitons in spin-orbit coupled Bose Einstein condensates （BECs） by a perturbation method. Starting with the one-dimensional Gross Pitaevskii equations, we derive a new KdV-like equation to which an approximate solution is obtained by assuming weak Raman coupling and strong spin orbit coupling. The derivation of the KdV-like equation may be useful to understand the properties of solitons excitation in spin-orbit coupled BECs. We find different types of moving solitons： dark-bright, bright bright and dark dark solitons. Interestingly, moving dark-dark soliton for attractive intra- and inter-species interactions is found, which depends on the Raman coupling. The amplitude and velocity of the moving solitons strongly depend on the Raman coupling and spin orbit coupling.

Head-on collision of ring dark solitons in Bose-Einstein condensates

The ring dark solitons and their head-on collisions in a Bose-Einstein condensates with thin disc-shaped potential are studied. It is shown that the system admits a solution with two concentric ring solitons, one moving inwards and the other moving outwards, which in small-amplitude limit, are described by the two cylindrical KdV equations in the respective reference frames. By using the extended Poincaré-Lighthill-Kuo perturbation method, the analytical phase shifts following the head-on collisions between two ring dark solitary waves are derived. It is shown that the phase shifts decrease with the radial coordinate r according to the r-1/3 law and depend on the initial soliton amplitude and radius.

Stability properties of vector solitons in two-component Bose-Einstein condensates with tunable interactions

By using a unified theory of the formation of various types of vector-solitons in two-component Bose-Einstein condensates with tunable interactions, we obtain a family of exact vector-soliton solutions for the coupled nonlinear Schrodinger equations. Moreover, the Bogoliubov equation shows that there exists stable dark soliton in specific situa- tions. Our results open up new ways in considerable experimental interest for the quantum control of multi-component Bose Einstein condensates.

Stabilised bright solitons in Bose-Einstein condensates in an expulsive parabolic and complex potential

The exact solitonic solutions of the one-dimensional nonlinear Schroedinger equation, which describes the dynamics of bright soliton in Bose-Einstein condensates with the time-dependent interaction in an expulsive parabolic and complex potential, are obtained by Darboux transformation. The results show that one can compress a bright soliton into an assumed peak of matter wave density by adusting the experimental parameter of the ratio of axial oscillation to radial oscillation or feeding parameter. Especially, when parameters satisfy the relation λ = 2γ the soliton is stable with time evolution without changing its shape and amplitude.

Merging and splitting dynamics between two bright solitons in dipolar Bose-Einstein condensates

We numerically study the interaction dynamics of two bright solitons with zero initial velocities in the one-dimensional dipolar Bose-Einstein condensates.Under different dipolar strengths,the two bright solitons can merge into a breathing wave,and then split or propagate constantly after several oscillating periods.We quantitatively study the breathing frequency of wave after merging and the asymmetry property of solitons after splitting,and analyze their formation mechanism by the system's energy evolution.Also,the change of initial phase difference brings distinct effects on the soliton interaction.Our results provide insight into the new dynamical phenomena in dipolar systems and enrich the understanding for interaction between dipolar solitons.

Bright and dark soliton solutions in growing Bose-Einstein condensates

This paper develops the Hirota method carefully for applying into the growing model of quasi-one-dimensional Bose Einstein condensations with attractive and repulsive interaction, respectively. After a tedious calculation it obtains the exact bright and dark soliton solutions analytically. It shows that the growing model has the important effect on the soliton amplitude and the time-dependent potential only contributes to the phase and phase velocity. A detailed analysis for the asymptotic behaviour of two-soliton solutions shows that the collision of two soliton is elastic.

Stable stripe and vortex solitons in two-dimensional spin-orbit coupled Bose-Einstein condensates

We present a flexible manipulation and control of solitons via Bose-Einstein condensates.In the presence of Rashba spin-orbit coupling and repulsive interactions within a harmonic potential,our investigation reveals the numerical local solutions within the system.By manipulating the strength of repulsive interactions and adjusting spin-orbit coupling while maintaining a zero-frequency rotation,diverse soliton structures emerge within the system.These include plane-wave solitons,two distinct types of stripe solitons,and odd petal solitons with both single and double layers.The stability of these solitons is intricately dependent on the varying strength of spin-orbit coupling.Specifically,stripe solitons can maintain a stable existence within regions characterized by enhanced spin-orbit coupling while petal solitons are unable to sustain a stable existence under similar conditions.When rotational frequency is introduced to the system,solitons undergo a transition from stripe solitons to a vortex array characterized by a sustained rotation.The rotational directions of clockwise and counterclockwise are non-equivalent owing to spin-orbit coupling.As a result,the properties of vortex solitons exhibit significant variation and are capable of maintaining a stable existence in the presence of repulsive interactions.

Bose-Einstein condensates in an eightfold symmetric optical lattice

We investigate the properties of Bose-Einstein condensates(BECs)in a two-dimensional quasi-periodic optical lattice(OL)with eightfold rotational symmetry by numerically solving the Gross-Pitaevskii equation.In a stationary external harmonic trapping potential,we first analyze the evolution of matter-wave interference pattern from periodic to quasiperiodic as the OL is changed continuously from four-fold periodic to eight-fold quasi-periodic.We also investigate the transport properties during this evolution for different interatomic interaction and lattice depth,and find that the BEC crosses over from ballistic diffusion to localization.Finally,we focus on the case of eightfold symmetric lattice and consider a global rotation imposed by the external trapping potential.The BEC shows vortex pattern with eightfold symmetry for slow rotation,becomes unstable for intermediate rotation,and exhibits annular solitons with approximate axial symmetry for fast rotation.These results can be readily demonstrated in experiments using the same configuration as in Phys.Rev.Lett.122110404(2019).

Special breathing structures induced by bright solitons collision in a binary dipolar Bose–Einstein condensates

We numerically investigate the breathing dynamics induced by collision between bright solitons in a binary dipolar Bose–Einstein condensates, whose dipole–dipole interaction and contact interaction are attractive. We identify three special breathing structures, such as snakelike special breathing structure, mixed breathing structure, and divide breathing structure.The characteristics of these breathing structures can be described by breathing frequency ?, maximum breathing amplitude A and lifetime τ, which can be manipulated by atomic number Ni and interspecies scattering length a12. Meanwhile, the above breathing structures can realize the process of quasi-transition with a reasonable Ni and a12. Additionally, the collision of two special breathing structures also can bring more abundant breathing dynamics. Our results provide a reference for the study of soliton interactions and deepen the understanding of soliton properties in a binary dipolar Bose–Einstein condensates.

Ground states, solitons and spin textures in spin-1 Bose-Einstein condensates

We present an overview of our recent theoretical studies on the quantum phenomena of the spin-1 Bose Einstein condensates, including the phase diagram, soliton solutions and the formation of the topological spin textures. A brief exploration of the effects of spin-orbit coupling on the ground-state properties is given. We put forward proposals by using the transmission spectra of an optical cavity to probe the quantum ground states： the ferromagnetic and polar phases. Quasi-one-dimension solitons and ring dark solitons are studied. It is predicted that characteristics of the magnetic solitons in optical lattice can be tuned by controlling the long-range light-induced and static magnetic dipole- dipole interactions; solutions of single-component magnetic and single-, two-, three-components polar solitons are found; ring dark solitons in spin-1 condensates are predicted to live longer lifetimes than that in their scalar counterparts. In the formation of spin textures, we have considered the theoretical model of a rapidly quenched and fast rotating trapped spin-1 Bose Einstein condensate, whose dynamics can be studied by solving the stochastic projected Gross-Pitaevskii equations. Spontaneous generation of nontrivial topological defects, such as the hexagonal lattice skyrmions and square lattice of half-quantized vortices was predicted. In particular, crystallization of merons （half skyrmions） can be generated in the presence of spin-orbit coupling.

Stationary and moving solitons in spin-orbit-coupled spin-1 Bose-Einstein condensates

We investigate the matter-wave sohtons in a spin-orbit-coupled spin-1 Bose-Einstein condensate us- ing a multiscale perturbation method. Beginning with the one-dimensional spin-orbit-coupled three- component Gross-Pitaevskii equations, we derive a single nonlinear SehrSdinger equation, which allows determination of the analytical soliton solutions of the system. Stationary and moving solitons in the system are derived. In particular, a parameter space for different existing soliton types is provided. It is shown that there exist only dark or bright sohtons when the spin-orbit coupling is weak, with the solitons depending onthe atomic interactions. However, when the spin-orbit coupling is strong, both dark and bright solitons exist, being determined by the Raman coupling. Our analytical solutions are confirmed by direct numerical simulations.

Dynamical nonlinear excitations induced by interaction quench in a two-dimensional box-trapped Bose-Einstein condensate

Manipulating nonlinear excitations,including solitons and vortices,is an essential topic in quantum many-body physics.A new progress in this direction is a protocol proposed in[Phys.Rev.Res.2043256(2020)]to produce dark solitons in a one-dimensional atomic Bose–Einstein condensate(BEC)by quenching inter-atomic interaction.Motivated by this work,we generalize the protocol to a two-dimensional BEC and investigate the generic scenario of its post-quench dynamics.For an isotropic disk trap with a hard-wall boundary,we find that successive inward-moving ring dark solitons(RDSs)can be induced from the edge,and the number of RDSs can be controlled by tuning the ratio of the after-and before-quench interaction strength across different critical values.The role of the quench played on the profiles of the density,phase,and sound velocity is also investigated.Due to the snake instability,the RDSs then become vortex–antivortex pairs with peculiar dynamics managed by the initial density and the after-quench interaction.By tuning the geometry of the box traps,demonstrated as polygonal ones,more subtle dynamics of solitons and vortices are enabled.Our proposed protocol and the discovered rich dynamical effects on nonlinear excitations can be realized in near future cold-atom experiments.

Three-dimensional solitons in two-component Bose–Einstein condensates

We investigate a kind of solitons in the two-component Bose-Einstein condensates with axisymmetric configurations in the R2 × S1 space. The corresponding topological structure is referred to as Hopfion. The spin texture differs from the conventional three-dimensional （3D） skyrmion and knot, which is characterized by two homotopy invariants. The stability of the Hopfion is verified numerically by evolving the Gross-Pitaevskii equations in imaginary time.

Nonautonomous deformed solitons in a Bose-Einstein condensate

We study exact single-soliton solutions of an attractive Bose-Einstein condensate governed by a one-dimensional nonautonomous Gross-Pitaevskii system. For several different forms of time-dependent atom-atom interaction and external parabolic potential which satisfy the exact integrability scenario, we construct a set of new analytical nonautonomous deformed-soliton solutions, including the macroscopic wave function and the position of soliton＇s center of mass. The soliton characteristics are modulated by the external field parameters and deformation factors related to the number of the condensed atoms and the initial conditions. The results suggest a simple and effective method for experimentally generating matter-wave deformed solitons and manipulating their motions.

Nonlinear dynamical stability of gap solitons in Bose-Einstein condensate loaded in a deformed honeycomb optical lattice

We investigate the existence and dynamical stability of multipole gap solitons in Bose-Einstein condensate loaded in a deformed honeycomb optical lattice.Honeycomb lattices possess a unique band structure,the first and second bands intersect at a set of so-called Dirac points.Deformation can result in the merging and disappearance of the Dirac points,and support the gap solitons.We find that the two-dimensional honeycomb optical lattices admit multipole gap solitons.These multipoles can have their bright solitary structures being in-phase or out-of-phase.We also investigate the linear stabilities and nonlinear stabilities of these gap solitons.These results have applications of the localized structures in nonlinear optics,and may helpful for exploiting topological properties of a deformed lattice.

Three-dimensional Bose Einstein condensate vortex solitons under optical lattice and harmonic confinements

We predict three-dimensional vortex solitons in a Bose-Einstein condensate under a complex potential,which is the combination of a two-dimensional parabolic trap along the transverse radial direction and a one-dimensional optical-lattice potential along the z axis direction.The vortex solitons are built in the form of a layer-chain structure made of several fundamental vortices along the optical-lattice direction.This has not been reported before in the three-dimensional Bose-Einstein condensate.By using a combination of the energy density functional method with direct numerical simulation,we find three-dimensional vortex solitons with topological charges χ=1,χ=2,and χ=3.Moreover,the macroscopic quantum tunneling and chirp phenomena of the vortex solitons are shown in the evolution.Therein,the occurrence of macroscopic quantum tunneling provides the possibility for the experimental realization of quantum tunneling.Specifically,we successfully manipulate the vortex solitons along the optical lattice direction.The stability limits for dragging the vortex solitons from an initial fixed position to a prescribed location are further pursued.