By means of analytical and numerical methods, we address the modulational instability (MI) in chiral condensates governed by the Gross-Pitaevskiiequation including the current nonlinearity. The analysis shows that this nonlinearity partly suppresses off the MI driven by the cubic self-focusing, although the current nonlinearity is not represented in the system's energy (although it modifies the momentum), hence it may be considered as zero-energy nonlinearity. Direct simulations demonstrate generation of trains of stochastically interacting chiral solitons by MI. In the ring-shaped setup, the MI creates a single traveling solitary wave. The sign of the current nonlinearity determines the direction of propagation of the emerging solitons.
We experimentally study universal nonequilibrium dynamics of two-dimensional atomic Bose gases quenched from repulsive to attractive interactions. We observe the manifestation of modulational instability that, instead of causing collapse, fragments a large two-dimensional superfluid into multiple wave packets universally around a threshold atom number necessary for the formation of Townes solitons. We confirm that the density distributions of quench-induced solitary waves are in excellent agreement with the stationary Townes profiles. Furthermore, our density measurements in the space and time…
By means of linear stability analysis (LSA) and direct numerical simulations of the coupled Gross-Pitaevskii(GP)equations, we address the impurity induced modulational instability (MI) and the associated nonlinear dynamics in Bose-Einstein condensates (BECs). We explore the dual role played by the impurities within the BECs -- the instigation of MI and the dissipation of the initially generated solitary waves. Because of the impurities, the repulsive BECs are even modulationally unstable and this tendency towards MI increases with increasing impurity fraction and superfluid-impurity coupling s…
We obtain general continuous-wave (CW)\ solutions in the model of a spinor positronium condensate in the absence of magnetic field. The CW solutions with both in-phase ($n=0$) and out-of-phase ($n=1$) spin components exist, with their ranges limited by the total particle density, $ρ$. In the limit of negligible population exchange between the spin components, the CW solutions are found to be stable or unstable, depending on the particle density of the para positronium. Ortho positronium, in the $F=1$ spinor state, forms a ferromagnetic condensate with stable in-phase CW solutions only. Subsequ…
We investigate the quench dynamics of a two-component Bose mixture and study the onset of modulational instability, which leads the system far from equilibrium. Analogous to the single-component counterpart, this phenomenon results in the creation of trains of bright solitons. We provide an analytical estimate of the number of solitons at long times after the quench for each of the two components based on the most unstable mode of the Bogoliubov spectrum, which agrees well with our simulations for quenches to the weak attractive regime when the two components possess equal intraspecies interac…
Nonlinearity management of matter-wave vector solitons of Bose-Einstein condensates in two dimensions
Physical-Technical Institute, Uzbek Academy of Sciences（乌兹别克斯坦科学院物理技术研究所）；Institute of Theoretical Physics, National University of Uzbekistan（乌兹别克斯坦国立大学理论物理研究所）；School of Science and Technology, Örebro University（厄勒布鲁大学理学院）；HMU Research Center, Institute of Emerging Technologies（新兴技术研究所HMU研究中心）
We demonstrate fast control of the interatomic interactions in a Bose-Einstein condensate by coherently coupling two atomic states with intra- and inter-state scattering lengths of opposite signs. We measure the elastic and inelastic scattering properties of the system and find good agreement with a theoretical model describing the interactions between dressed states. In the attractive regime, we observe the formation of bright solitons formed by dressed-state atoms. Finally, we study the response of the system to an interaction quench from repulsive to attractive values, and observe how the r…
An overview is given of basic models combining discreteness in their linear parts (i.e. the models are built as dynamical lattices) and nonlinearity acting at sites of the lattices or between the sites. The considered systems include the Toda and Frenkel-Kontorova lattices (including their dissipative versions), as well as equations of the discrete nonlinear Schroedinger (DNLS) and Ablowitz-Ladik (AL) types, and DNLS-AL combination in the form of the Salerno model. The interplay of discreteness and nonlinearity gives rise to a variety of states, most important ones being self-trapped discrete …
Solitons supported by singular spatial modulation of the Kerr nonlinearity
我们引入了一种基于一维非线性薛定谔方程（NLSE）的设置，其中自聚焦（SF）立方项由坐标的奇异函数|x| ^{-a}调制。它还可以与均匀自散焦（SDF）非线性背景相结合，并与类似的奇异排斥线性势相结合。该装置可以在光学和BEC中实现，旨在扩展NLSE中孤子的存在性和稳定性的一般分析。基本孤子的结果得到了解析和数值验证。孤子具有准尖点形状，二阶导数在中心发散，并且在0 < a < 1的整个存在范围内是稳定的。偶极（奇）孤子也被发现。它们在无限域内是不稳定的，但在半无限域内是稳定的。在SDF背景的存在下，存在两个基本孤子的子族，一个稳定的和一个不稳定的，它们一起存在于一个阈值以上的范数（孤子的总功率）。该系统还包括奇异排斥线性势，模拟分数维0 < D < 1的均匀空间中的孤子。一个二维扩展的系统，二次非线性的基础上，制定太。
