Quantum-torque-induced breaking of magnetic interfaces in ultracold gases

Bose-Einstein Condensates (BECs) with multiple internal states allow the study of spin dynamics and magnetic phenomena on a flexible platform. Thanks to a novel experimental apparatus [1,2], we studied the spin dynamics of an elongated coherently-coupled two-component BEC in a previously inaccessible regime where the spin dynamics is both non-homogenous and non-dissipative.

In this work, we realized the atomic analogue of a magnetic material in a transverse field with spatially inhomogeneous magnetic anisotropy. Here two different dynamical regimes naturally develop, respectively where the external field dominates over the magnetic anisotropy and vice versa, at the interface of which the spin dynamics changes abruptly. This interface then breaks due to the onset of quantum torque, analogous to the Heisenberg exchange term in magnetic materials, creating highly energetic magnetic waves that disrupts the local dynamics [3].

[1] A. Farolfi et al., Rev. Scient. Instr. 90, 115114 (2019)

[2] A. Farolfi et al., arxiv:2101.12643

[3] A. Farolfi et al., arXiv:2011.04271