Observation of an Alice ring in a Bose–Einstein condensate

Abstract

Monopoles and vortices are fundamental topological excitations that appear in physical systems spanning enormous scales of size and energy, from the vastness of the early universe to tiny laboratory droplets of nematic liquid crystals and ultracold gases. Although the topologies of vortices and monopoles are distinct from one another, under certain circumstances a monopole can spontaneously and continuously deform into a vortex ring with the curious property that monopoles passing through it are converted into anti-monopoles. However, the observation of such Alice rings has remained a major challenge, due to the scarcity of experimentally accessible monopoles in continuous fields. Here, we present experimental evidence of an Alice ring resulting from the decay of a topological monopole defect in a dilute gaseous 87Rb Bose–Einstein condensate. Our results, in agreement with detailed first-principles simulations, provide an unprecedented opportunity to explore the unique features of a composite excitation that combines the topological features of both a monopole and a vortex ring.

Physics news on the Internet: October 2023

“…Analogues of Alice strings have been observed in superfluid liquids and liquid crystals. A Blinova (Amherst College and University of Massachusetts Amherst, USA) and her coauthors have become the first to observe closed Alice strings in the form of rings in a Bose±Einstein condensate of 87 Rb atoms in an optical trap [10]. The magnetic field generated by Helmholtz coils led to the formation of singular vortex points (monopoles) carrying topological charges and turning into Alice rings.…”