Abstract Spin‐orbit coupling (SOC) has broad relevances and its interplay with other interactions and potential geometry may induce novel quantum states. This work explores exotic quantum states emerging in the ground state (GS) of a strongly‐correlated spin‐1 Bose–Einstein condensate confined in 2D concentric annular traps with SOC. In the antiferromagnetic case, the GS density manifests various patterns of distributions, including facial‐makeup states, petal states, topological fissure states, multiple‐half‐ring states and property‐distinguished vertical and horizontal stripe states. A peculiar phenomenon of density‐phase separation is noticed in the sense that the variations of density and phase tend to be independent. In ferromagnetic case, the GS exhibits a semi‐circular or half‐disk status of density embedded with vortices and antivortices. The spin distribution can self‐arrange into an array of half‐skyrmions and a half‐antiskyrmion fence separating vortex‐antivortex pairs is also found. This study indicates that one can manipulate the emergence of exotic quantum states and the locations of the topological defects via the interplay of the SOC, interactions and potential geometry and the abundant state variations might also provide potential resources for quantum metrology.
Abstract Spin‐orbit coupling (SOC) has broad relevances and its interplay with other interactions and potential geometry may induce novel quantum states. This work explores exotic quantum states emerging in the ground state (GS) of a strongly‐correlated spin‐1 Bose–Einstein condensate confined in 2D concentric annular traps with SOC. In the antiferromagnetic case, the GS density manifests various patterns of distributions, including facial‐makeup states, petal states, topological fissure states, multiple‐half‐ring states and property‐distinguished vertical and horizontal stripe states. A peculiar phenomenon of density‐phase separation is noticed in the sense that the variations of density and phase tend to be independent. In ferromagnetic case, the GS exhibits a semi‐circular or half‐disk status of density embedded with vortices and antivortices. The spin distribution can self‐arrange into an array of half‐skyrmions and a half‐antiskyrmion fence separating vortex‐antivortex pairs is also found. This study indicates that one can manipulate the emergence of exotic quantum states and the locations of the topological defects via the interplay of the SOC, interactions and potential geometry and the abundant state variations might also provide potential resources for quantum metrology.
Abstract Dipole–dipole interaction (DDI) possesses characteristics different from the conventional isotropic s‐wave interaction in Bose‐Einstein condensates (BECs). The interplay of DDI with spin‐orbit coupling (SOC) and rotation may induce novel quantum properties. This work systematically analyzes the effects of the DDI, Weyl‐like SOC, rotation and trap anharmonicity in the ground state of two‐component BECs. The interplay of these factors leads to a kaleidoscope of quantum states, emerging in quantum defects, droplets, wheel and ring forms of density distributions, accompanied with transitions of topology of density, and manifesting a critical behavior around a revealed density‐collapse point. A bunch of exotic spin topological structures are shown, including centric vortex surrounded by layers of spin flows, compound topological structure of edge defect, and various coexistence states of skyrmions with different topological charges. In particular, quarter skyrmions and other possible fractional skyrmions are found. Rashba‐type SOC and Weyl‐like SOC are also compared. The study implies that one can manipulate both the density topology and the spin topological structure via these tunable parameters in BECs. The abundant variations of the topological structures and particularly the revealed critical behavior may provide quantum resources for potential applications in quantum metrology.
Abstract We consider the topological defects and spin structures of spin-1 Bose–Einstein condensates with spin–orbit coupling (SOC) and dipole–dipole interaction (DDI) in a rotating harmonic plus quartic trap. The combined effects of SOC, DDI and rotation on the ground-state phases of the system are analyzed. Our results show that for fixed rotation frequency structural phase transitions can be achieved by adjusting the magnitudes of the SOC and DDI. A ground-state phase diagram is given as a function of the SOC and DDI strengths. It is shown that the system exhibits rich quantum phases including vortex string phase with isolated density peaks (DPs), triangular (square) vortex lattice phase with DPs, checkerboard phase, and stripe phase with hidden vortices and antivortices. For given SOC and DDI strengths, the system can display pentagonal vortex lattice with DPs, vortex necklace with DPs, and exotic topological structure composed of multi-layer visible vortex necklaces, a hidden giant vortex and hidden vortex necklaces, depending on the rotation frequency. In addition, the system sustains fascinating novel spin textures and skyrmion excitations, such as an antiskyrmion pair, antiskyrmion-half-antiskyrmion (antiskyrmion–antimeron) cluster, skyrmion–antiskyrmion lattice, skyrmion–antiskyrmion cluster, skyrmion–antiskyrmion–meron–antimeron lattice, double-layer half-antiskyrmion necklaces, and composite giant-antiskyrmion–antimeron necklaces.
Abstract We consider the ground-state properties of Rashba spin–orbit-coupled pseudo-spin-1/2 Bose–Einstein condensates (BECs) in a rotating two-dimensional (2D) toroidal trap. In the absence of spin–orbit coupling (SOC), the increasing rotation frequency enhances the creation of giant vortices for the initially miscible BECs, while it can lead to the formation of semiring density patterns with irregular hidden vortex structures for the initially immiscible BECs. Without rotation, strong 2D isotropic SOC yields a heliciform-stripe phase for the initially immiscible BECs. Combined effects of rotation, SOC, and interatomic interactions on the vortex structures and typical spin textures of the ground state of the system are discussed systematically. In particular, for a fixed rotation frequency above the critical value, the increasing isotropic SOC favors a visible vortex necklace in each component which is accompanied by a hidden giant vortex plus a (several) hidden vortex necklace(s) in the central region. In the case of one-dimensional anisotropic SOC, large SOC strength results in the generation of hidden linear vortex string and the transition from initial component separation (component mixing) to component mixing (component separation). Furthermore, the peculiar spin textures including skyrmion lattice, skyrmion pair and skyrmion string are revealed in this system.
We study the ground-state phases of spin–orbit coupled spin-2 Bose–Einstein condensates in a two-dimensional concentrically coupled annular trap with the attractive and repulsive spin-exchange interactions, respectively. For the system with the attractive spin-exchange interaction, the ground-state phase densities in the inner ring show the bright solitons along the azimuthal direction with the weak spin–orbit coupling strength and the vortex line along the radial direction with the strong spin–orbit coupling strength. For the system with the repulsive spin-exchange interaction, the necklace-like state is shown. The number of petals of the necklace-like state continuous growth as the spin–orbit coupling strength enhanced. The momentum distributions of the ground-state phases are also studied.
Abstract We investigate the topological excitations of rotating spin-1 ferromagnetic Bose–Einstein condensates with spin–orbit coupling (SOC) in an in-plane quadrupole field. Such a system sustains a rich variety of exotic vortex structures due to the spinor order parameter and the interplay among in-plane quadrupole field, SOC, rotation, and interatomic interaction. For the nonrotating case, with the increase of the quadrupole field strength, the system experiences a transition from a coreless polar-core vortex with a bright soliton to a singular polar-core vortex with a density hole. Without rotation but with a fixed quadrupole field, when the SOC strength increases, the system transforms from a central Mermin–Ho vortex into a criss-crossed vortex–antivortex string lattice. For the rotating case, we give a phase diagram with respect to the quadrupole field strength and the SOC strength. It is shown that the rotating system supports four typical quantum phases: vortex necklace, diagonal vortex chain cluster, single diagonal vortex chain, and few vortex states. Furthermore, the system favors novel spin textures and skyrmion excitations including an antiskyrmion, a criss-crossed half-skyrmion–half-antiskyrmion lattice, a skyrmion-meron necklace, a symmetric half-skyrmion lattice, and an asymmetric skyrmion-meron lattice.
Abstract The ground-state properties of a spin–orbit-coupled spin-1 Bose–Einstein condensate (BEC) in a toroidal trap are investigated. The exotic ground states, such as the necklace state, the persistent flow and even the vortex state, for the three components in the system are induced by adjustable external parameters. It is found that the petal number of the necklace states is increased with increasing the intensity of the spin–orbit coupling (SOC), and the anisotropy of the SOC can be used to control the structure of the ground states. The rotation of the condensate induced by the external field makes the densities of the three components asymmetric and tends to transform the necklace state to the persistent flow. The radius of the toroidal potential is another degree of freedom for manipulating the necklace state. In addition, the transition between the necklace state and the vortex, intermediated by the persistent flow, can be controlled by the ratio of the density-density and spin-exchange interactions. All of above results enrich our knowledge about the properties of the ground states of spin-1 BEC trapped in the toroidal trap.