Transverse Spin Dynamics in the Anisotropic Heisenberg Model Realized with Ultracold Atoms

In Heisenberg models with exchange anisotropy, transverse spin components are not conserved and can decay not only by transport, but also by dephasing. Here, we utilize ultracold atoms to simulate the dynamics of 1D Heisenberg spin chains and observe fast, local spin decay controlled by the anisotropy. However, even for isotropic interactions, we observe dephasing due to a new effect: an effective magnetic field created by superexchange. If spatially uniform, it leads only to uniform spin precession and is, therefore, typically ignored. However, we show through experimental studies and extensive numerical simulations how this superexchange-generated field is relevant and leads to additional dephasing mechanisms over the exchange anisotropy: There is dephasing due to (i) inhomogeneity of the effective field from variations of lattice depth between chains; (ii) a twofold reduction of the field at the edges of finite chains; and (iii) fluctuations of the effective field due to the presence of mobile holes in the system. The latter is a new coupling mechanism between holes and magnons. All these dephasing mechanisms have not been observed before with ultracold atoms and illustrate basic properties of the underlying Hubbard model.

Automated summary

The study utilizes ultracold atoms to simulate the dynamics of 1D Heisenberg spin chains, observing fast spin decay controlled by anisotropy and dephasing caused by the effective magnetic field from superexchange. The research also reveals new dephasing mechanisms, including inhomogeneity of the effective field, reduction of field at chain edges, and fluctuations due to mobile holes. These mechanisms have not been previously observed with ultracold atoms, providing insights into the Hubbard model.