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.

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用超冷原子实现的各向异性海森堡模型中的横向自旋动力学

在具有交换各向异性的海森堡模型中，横向自旋分量不守恒，不仅可以通过传输衰减，还可以通过去相位衰减。在这里，我们利用超冷原子来模拟一维海森堡自旋链的动力学，并观察由各向异性控制的快速局部自旋衰减。然而，即使对于各向同性相互作用，我们也观察到由​​于一种新效应的移相：超交换产生的有效磁场。如果空间均匀，它只会导致均匀的自旋进动，因此通常被忽略。然而，我们通过实验研究和广泛的数值模拟展示了这种超交换产生的场是如何相关的，并导致交换各向异性的额外相移机制：由于（i）链之间晶格深度变化导致的有效场不均匀；(ii) 有限链边缘的场的两倍减少；(iii) 由于系统中存在移动孔，有效场的波动。后者是孔与磁振子之间新的耦合机制。所有这些去相机制之前都没有在超冷原子中观察到，并说明了基本的哈伯德模型的基本特性。