近日，美国哈佛大学的Markus Greiner及其研究团队取得一项新进展。经过不懈努力，他们观测到费米-哈伯德量子模拟器中的Nagaoka极化子。相关研究成果已于2024年5月8日在国际权威学术期刊《自然》上发表。

该研究团队证明了Nagaoka 极化子在三角形光学晶格中用强相互作用费米子实现的哈伯德系统中的出现。利用量子气体显微镜，研究人员将这些极化子成像为粒子掺杂剂周围的扩展铁磁气泡，这些气泡是由相干掺杂剂运动和自旋交换的局部相互作用产生的。相比之下，由于三角形几何结构引起的动力学阻挫促进了空穴掺杂剂周围的反铁磁极化子。这项研究预示着对强关联系统和超大尺寸系统中电荷运动驱动的奇异量子相的探索，这对数值模拟而言极具挑战性。

据悉，量子干涉可以显著地改变物质多体相的性质。在哈伯德模型中，Nagaoka证明了引入单个流动电荷可以通过路径干涉将顺磁绝缘体转变为铁磁体。然而，由单独成像的掺杂剂引起的这种动力学磁性的微观观察迄今为止还难以捉摸。

附：英文原文

Title: Observation of Nagaoka polarons in a Fermi–Hubbard quantum simulator

Author: Lebrat, Martin, Xu, Muqing, Kendrick, Lev Haldar, Kale, Anant, Gang, Youqi, Seetharaman, Pranav, Morera, Ivan, Khatami, Ehsan, Demler, Eugene, Greiner, Markus

Issue&Volume: 2024-05-08

Abstract: Quantum interference can deeply alter the nature of many-body phases of matter. In the case of the Hubbard model, Nagaoka proved that introducing a single itinerant charge can transform a paramagnetic insulator into a ferromagnet through path interference. However, a microscopic observation of this kinetic magnetism induced by individually imaged dopants has been so far elusive. Here we demonstrate the emergence of Nagaoka polarons in a Hubbard system realized with strongly interacting fermions in a triangular optical lattice. Using quantum gas microscopy, we image these polarons as extended ferromagnetic bubbles around particle dopants arising from the local interplay of coherent dopant motion and spin exchange. By contrast, kinetic frustration due to the triangular geometry promotes antiferromagnetic polarons around hole dopants. Our work augurs the exploration of exotic quantum phases driven by charge motion in strongly correlated systems and over sizes that are challenging for numerical simulation.

DOI: 10.1038/s41586-024-07272-9

Source: https://www.nature.com/articles/s41586-024-07272-9