Giuseppe Baio (University of East Anglia) gives a webinar on ‘Monopoles, Alice rings and topological interfaces in spinor Bose-Einstein condensates’.

Recent experimental advancements in ultracold atoms are leading to the controlled creation of complex topological excitations in spinor Bose-Einstein condensates (BECs) [1]. In this webinar, I will address defects and their dynamics in a spin-2 BECs, where the rich variety of order-parameter symmetries allows exotic phenomena such as fractional vortex charges, monopoles, and non-singular spin textures. In particular, I will show how energy relaxation causes a monopole in the uniaxial-nematic phase to deform into a spin-Alice ring, exhibiting a composite core with distinct short- and long-distance topologies [2]. Numerical simulations reveal dynamical oscillations between the spin-Alice ring and a split-core hedgehog configuration. Moreover, I will also address hybrid defect connections and their stability across optically induced topological interfaces in uniaxial-to-biaxial nematic (UN-BN), cyclic-to-ferromagnetic (C-FM), and cyclic-to-biaxial nematic (C-BN) phases, where a sudden topology change occurs in a fashion similar to that of early-universe theories [3].

[1] Xiao, Y. et al., Nat. Commun. 13, 4635 (2022).

[2] Baio, G. & Borgh M. O., arXiv:2401.04103 (2024).

[3] Baio, G. et al., Phys. Rev. Research 6, 013046 (2024).