Walter Anne-Sophie, Zhu Zijie, Gächter Marius, Minguzzi Joaquín, Roschinski Stephan, Sandholzer Kilian, Viebahn Konrad, Esslinger Tilman
Institute for Quantum Electronics & Quantum Center, ETH Zurich, Zurich, Switzerland.
Nat Phys. 2023;19(10):1471-1475. doi: 10.1038/s41567-023-02145-w. Epub 2023 Jul 24.
Geometric properties of wave functions can explain the appearance of topological invariants in many condensed-matter and quantum systems. For example, topological invariants describe the plateaux observed in the quantized Hall effect and the pumped charge in its dynamic analogue-the Thouless pump. However, the presence of interparticle interactions can affect the topology of a material, invalidating the idealized formulation in terms of Bloch waves. Despite pioneering experiments in different platforms, the study of topological matter under variations in interparticle interactions has proven challenging. Here we experimentally realize a topological Thouless pump with fully tuneable Hubbard interactions in an optical lattice and observe regimes with robust pumping, as well as an interaction-induced breakdown. We confirm the pump's robustness against interactions that are smaller than the protecting gap for both repulsive and attractive interactions. Furthermore, we identify that bound pairs of fermions are responsible for quantized transport at strongly attractive interactions. However, for strong repulsive interactions, topological pumping breaks down, but we show how to reinstate it by modifying the pump trajectory. Our results will prove useful for further investigations of interacting topological matter, including edge effects and interaction-induced topological phases.
波函数的几何性质可以解释许多凝聚态和量子系统中拓扑不变量的出现。例如，拓扑不变量描述了在量子霍尔效应中观察到的平台以及其动态类似物—— Thouless泵中的泵浦电荷。然而，粒子间相互作用的存在会影响材料的拓扑结构，使基于布洛赫波的理想化表述失效。尽管在不同平台上有开创性的实验，但研究粒子间相互作用变化下的拓扑物质已被证明具有挑战性。在这里，我们通过实验在光学晶格中实现了具有完全可调Hubbard相互作用的拓扑Thouless泵，并观察到了具有稳健泵浦的区域以及相互作用诱导的击穿现象。我们证实了该泵对于小于保护能隙的相互作用（包括排斥和吸引相互作用）具有稳健性。此外，我们确定费米子束缚对在强吸引相互作用下负责量子化输运。然而，对于强排斥相互作用，拓扑泵浦会失效，但我们展示了如何通过修改泵浦轨迹来恢复它。我们的结果将有助于进一步研究相互作用的拓扑物质，包括边缘效应和相互作用诱导的拓扑相。
