Properties of a nematic spin vortex in an antiferromagnetic spin-1 Bose-Einstein condensate

Fractional-charge vortex dipoles in spinor Bose-Einstein condensates

We theoretically and numerically investigate the generation of fractional-charge vortex dipoles in spinor condensates with non-zero magnetization. We find that in the antiferromagnetic phase of spin-1 and spin-2 and the cyclic phase of spin-2 condensate with non-zero magnetization coupling of the density (phonon) and a spin-excitation mode results in two critical speeds for vortex-antivortex pair creation in the condensate. As a result, a Gaussian obstacle potential moving across the antiferromagnetic spin-1 or spin-2 and cyclic spin-2 spinor condensates with non-zero magnetization can lead to…

Anderson tower of states and nematic order of spin-1 bosonic atoms on a 2D lattice

We investigate the structure of the spectrum of antiferromagnetically coupled spin-1 bosons on a square lattice using degenerate perturbation theory and exact diagonalizations of finite clusters. We show that the superfluid phase develops an Anderson tower of states typical of nematic long-range order with broken SU(2) symmetry.We further show that this order persists into the Mott insulating phase down to zero hopping for one boson per site, and down to a critical hopping for two bosons per site, in agreement with mean-field and Quantum Monte Carlo results. The connection with the transition …

Topologically protected vortex knots and links

We propose a class of tangled vortex structures, tied from non-Abelian topological vortices, which are immune against decaying through local reconnections and strand crossings that are allowed by the system. We refer to such structures as being topologically protected. We then turn our attention to topological vortices classified by the quaternion group $Q_8$ ($Q_8$-colored links), which are realizable in systems consisting either of the biaxial nematic or the cyclic phase of a spin-2 Bose--Einstein condensate, or of biaxial nematic liquid crystal, and prove the existence of topologically prot…

光量子流体三角涡旋晶格中的反铁磁Ising模型

Antiferromagnetic Ising model in a triangular vortex lattice of quantum fluids of light

基于exciton-polariton凝聚体的光量子流体构建三角涡旋晶格，发现涡旋轨道角动量自发反平行排列形成人工反铁磁性，其图案与反铁磁Ising系统低能解相关，为可控有序涡旋阵列提供新途径。

Vortex Tiling in a Spin-2 Spinor Bose-Einstein Condensate

We point out that the internal spin symmetry of the order parameter manifests itself at the core of a fractional vortex in real space without spin-orbit coupling. Such symmetry breaking arises from a topological constraint and the commensurability between spin symmetries of the order parameters inside and outside the core. Our prediction can be applied to probe the cyclic order parameter in a rotating spin-2 $^{87}$Rb condensate as a non-circular vortex core in a biaxial nematic state.

Phase diagrams and multistep condensations of spin-1 bosonic gases in optical lattices

Motivated by recent experimental processes, we systemically investigate strongly correlated spin-1 ultracold bosons trapped in a three-dimensional optical lattice in the presence of an external magnetic field. Based on a recently developed bosonic dynamical mean-field theory (BDMFT), we map out complete phase diagrams of the system for both antiferromagnetic and ferromagnetic interactions, where various phases are found as a result of the interplay of spin-dependent interaction and quadratic Zeeman energy. For antiferromagnetic interactions, the system demonstrates competing magnetic orders, i…

Magnon pairing in quantum spin nematic

Competing ferro- and antiferromagnetic exchange interactions may lead to the formation of bound magnon pairs in the high-field phase of a frustrated quantum magnet. With decreasing field, magnon pairs undergo a Bose-condensation prior to the onset of a conventional one-magnon instability. We develop an analytical approach to study the zero-temperature properties of the magnon-pair condensate, which is a bosonic analog of the BCS superconductors. Representation of the condensate wave-function in terms of the coherent bosonic states reveals the spin-nematic symmetry of the ground-state and allow…

spin-2 Bose-Einstein condensates 中单极子与 Alice 环的复合核

Composite cores of monopoles and Alice rings in spin-2 Bose-Einstein condensates

本文通过数值模拟证明，spin-2 Bose-Einstein condensates 中点缺陷能量弛豫形变为具有复合核结构的 spin-Alice 环，并揭示了其在不同相中的动力学振荡与拓扑特征。

Energetic stability of coreless vortices in spin-1 Bose-Einstein condensates with conserved magnetization

We show that conservation of longitudinal magnetization in a spinor condensate provides a stabilizing mechanism for a coreless vortex phase-imprinted on a polar condensate. The stable vortex can form a composite topological defect with distinct small- and large-distance topology: the inner ferromagnetic coreless vortex continuously deforms toward an outer singular, singly quantized polar vortex. A similar mechanism can also stabilize a nonsingular nematic texture in the polar phase. A weak magnetization is shown to destabilize a coreless vortex in the ferromagnetic phase.

实验可实现系统中的拓扑保护涡旋结

Topologically Protected Vortex Knots in an Experimentally Realizable System

本研究利用自旋-2 BEC循环相和弯芯向列液晶四面体相中的非阿贝尔涡旋，构造出不能经交叉重连衰变为未链接环缺陷的拓扑保护涡旋结。