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. Strong interactions in many-body quantum systems complicate the interpretation of charge transport in such materials. To shed light on this problem, we study transport in a clean quantum system: ultracold lithium-6 in a two-dimensional optical lattice, a testing ground for strong interaction physics in the Fermi-Hubbard model. We determine the diffusion constant by measuring the relaxation of an imposed density modulation and modeling its decay hydrodynamically. The diffusion constant is converted to a resistivity by using the Nernst-Einstein relation. That resistivity exhibits a linear temperature dependence and shows no evidence of saturation, two characteristic signatures of a bad metal. The techniques we developed in this study may be applied to measurements of other transport quantities, including the optical conductivity and thermopower.

中文翻译：

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冷原子费米-哈伯德系统中的不良金属输运

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。多体量子系统中的强相互作用使对此类材料中电荷传输的解释复杂化。为了阐明这个问题，我们研究了清洁量子系统中的传输：二维光学晶格中的超冷锂 6，这是费米-哈伯德模型中强相互作用物理学的试验场。我们通过测量强加密度调制的弛豫并对其衰减进行流体动力学建模来确定扩散常数。通过使用 Nernst-Einstein 关系将扩散常数转换为电阻率。该电阻率表现出线性温度相关性，并且没有饱和迹象，这是劣质金属的两个特征特征。