Simulating transport with cold atoms Much can be learned about the nature of a solid from how charge and spin propagate through it. Transport experiments can also be performed in quantum simulators such as cold atom systems, in which individual atoms can be imaged using quantum microscopes. Now, two groups have investigated transport in the so-called Fermi-Hubbard model using a two-dimensional optical lattice filled with one fermionic atom per site (see the Perspective by Brantut). Moving away from half-filling to enable charge transport, Brown et al. found that the resistivity had a linear temperature dependence, not unlike that seen in the strange metal phase of cuprate superconductors. In a complementary study on spin transport, Nichols et al. observed spin diffusion driven by superexchange coupling. Science, this issue p. 379, p. 383; see also p. 344 Atomic transport in a 2D optical lattice is investigated in the strongly interacting regime at or near half-filling. Strongly correlated materials are expected to feature unconventional transport properties, such that charge, spin, and heat conduction are potentially independent probes of the dynamics. In contrast to charge transport, the measurement of spin transport in such materials is highly challenging. We observed spin conduction and diffusion in a system of ultracold fermionic atoms that realizes the half-filled Fermi-Hubbard model. For strong interactions, spin diffusion is driven by super-exchange and doublon-hole–assisted tunneling, and strongly violates the quantum limit of charge diffusion. The technique developed in this work can be extended to finite doping, which can shed light on the complex interplay between spin and charge in the Hubbard model.

中文翻译：

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超冷费米子莫特绝缘体中的自旋输运

模拟冷原子的传输，可以从电荷和自旋如何通过固体传播来了解固体的性质。传输实验也可以在量子模拟器中进行，例如冷原子系统，其中单个原子可以使用量子显微镜进行成像。现在，两个小组使用每个位点填充一个费米子原子的二维光学晶格研究了所谓的费米-哈伯德模型中的传输（参见 Brantut 的观点）。远离半填充以实现电荷传输，Brown 等人。发现电阻率具有线性温度依赖性，与在铜酸盐超导体的奇怪金属相中看到的情况不同。在自旋输运的补充研究中，Nichols 等人。观察到由超交换耦合驱动的自旋扩散。科学，这个问题 p。379 页。383; 另见第。344 在半填充或接近半填充的强相互作用状态下研究了二维光学晶格中的原子输运。强相关材料预计具有非常规传输特性，例如电荷、自旋和热传导是动力学的潜在独立探针。与电荷传输相反，测量此类材料中的自旋传输极具挑战性。我们在实现半填充费米-哈伯德模型的超冷费米子原子系统中观察到自旋传导和扩散。对于强相互作用，自旋扩散是由超交换和双孔辅助隧穿驱动的，并且强烈违反了电荷扩散的量子极限。这项工作中开发的技术可以扩展到有限掺杂，