New type of Bose-Einstein condensation of cold atoms with effective spin-orbit interactions

Brandon Anderson, Tudor D. Stanescu, Victor M. Galitski

Congjun Wu, Ian Mondragon-Shem, Xiang-Fa Zhou

According to the “no-node" theorem, the many-body ground state wavefunctions of conventional Bose—Einstein condensations (BEC) are positive-definite, thus time-reversal symmetry cannot be spontaneously broken. We find that multi-component bosons with spin-orbit coupling provide an unconventional type of BECs beyond this paradigm. We focus on a subtle case of isotropic Rashba spin-orbit coupling and the spin-independent interaction. In the limit of the weak confining potential, the condensate wavefunctions are frustrated at the Hartree—Fock level due to the degeneracy of the Rashba ring. Quantum zero-point energy selects the spin-spiral type condensate through the “order-from-disorder" mechanism. In a strong harmonic confining trap, the condensate spontaneously generates a half-quantum vortex combined with the skyrmion type of spin texture. In both cases, time-reversal symmetry is spontaneously broken. These phenomena can be realized in both cold atom systems with artificial spin-orbit couplings generated from atom-laser interactions and exciton condensates in semi-conductor systems.

Chunyan Li, Fangwei Ye, Xinghong Chen +3 more

We address the impact of spin-orbit coupling on the existence and properties of topological edge states of cold neutral atoms and Bose-Einstein condensates loaded in honeycomb Zeeman lattices---lattices where the spinor components are placed in potentials having opposite signs. We find that the type of spin-orbit-coupling mechanism has profound effect on the emergence of topological edge states. We also reveal that edge states persist when interatomic interactions are present and that they become metastable in Bose-Einstein condensates.

Y.-J. Lin, Karina Jiménez-García, Ian B. Spielman

Congjun Wu, Ian Mondragon-Shem

According to the no-node theorem, many-body ground state wavefunctions of conventional Bose-Einstein condensations (BEC) are positive-definite, thus time-reversal symmetry cannot be spontaneously broken. We find that multi-component bosons with spin-orbit coupling provide an unconventional type of BECs beyond this paradigm. We focus on the subtle case of isotropic Rashba spin-orbit coupling and the spin-independent interaction. In the limit of the weak confining potential, the condensate wavefunctions are frustrated at the Hartree-Fock level due to the degeneracy of the Rashba ring. Quantum zero-point energy selects the spin-spiral type condensate through the order-from-disorder mechanism. In a strong harmonic confining trap, the condensate spontaneously generates a half-quantum vortex combined with the skyrmion type of spin texture. In both cases, time-reversal symmetry is spontaneously broken. These phenomena can be realized in both cold atom systems with artificial spin-orbit couplings generated from atom-laser interactions and exciton condensates in semi-conductor systems.

Jeffrey Ting Fung Poon, Xiong-Jun Liu