Novel Ferromagnetic Domains and Quantum Criticality with Bose Condensates in a Shaken Optical Lattice

虽然原子长期以来一直被认为是我们所看到的世界和我们生活的环境的组成部分，但它们在低温下的行为一直让我们感到惊讶。例子包括无摩擦流动的超流体和允许读取、写入和存储大量信息的量子磁性材料。最近由首席研究员领导的一项研究表明，当激光束来回摇动原子时，超流动性和铁磁性（条形磁铁中的磁性类型）同时表现出来，就像乒乓球在湖面上荡起涟漪一样。在原子超流体中观察到的磁畴的有趣动力学提示了在量子体制中有效存储和处理信息的新策略。该项目的主要科学目标是在二维晶格中模拟和研究一种新型的四极磁铁，它比传统材料中的两极（南极和北极）磁性具有更丰富的特性。科学项目得到了S.M.A.R.T.（科学、数学和研究培训）项目的广泛推广。当原子超流体被转移到由重叠的两个垂直的光驻波产生的二维振荡光学晶格中时，将出现所提出的四极磁相。当振动幅度被仔细调整到一个临界值以上时，超流体预计会分裂成4个具有铁磁相互作用的极。4极畴的形成将通过原子样品的直接原位成像来检测和研究。与传统的2极磁体相比，4极磁体提供了新的域和顶点结构，并且与图论中的四色定理和统计物理中的波茨模型有独特的关系。此外，相变到铁磁相与各种量子现象有关，包括Rashba超流体、Berezinskii-Kosterlitz-Thouless相变和Kibble-Zurek机制。对这种量子物理学的探索可能会有学术和实践上的回报，包括发展一个理论框架来理解量子临界动力学，模拟n极铁磁磁体，制造可编程磁性材料，甚至可能是量子信息存储和处理。

While atoms have been long recognized as the building blocks of the world we see and the environment we live in, their behavior at low temperatures has never ceased to surprise us. Examples include superfluids that flow without friction and quantum magnetic materials that permit read, write and storage of ample information. A recent work led by the principal investigator showed that both superfluidity and ferromagnetism (the type of magnetism in bar magnets) manifest simultaneously in atoms when shaken back and forth by laser beams, like ping-pong balls riding the ripples on a lake. The intriguing dynamics of magnetic domains observed in the atomic superfluids suggests new strategies to efficiently store and process information in the quantum regime. The major science goal of this project is to simulate and study a new type of 4-pole magnet in a two-dimensional lattice, which promises much richer properties than the 2-pole (south and north pole) magnetism in conventional materials. The science program is complimented by an extensive outreach effort under the S.M.A.R.T. (Science, Mathematics, And Research Training) project. The proposed 4-pole magnetic phase will arise when an atomic superfluid is transferred into a two-dimensional shaken optical lattice, generated by overlapping two perpendicular optical standing waves. When the shaking amplitude is carefully tuned above a critical value, the superfluid is anticipated to split into 4 poles with ferromagnetic interactions. The formation of the 4-pole domain will be detected and studied by direct in situ imaging of the atomic sample. Compared to the conventional 2-pole magnets, the 4-pole magnets offer novel domain and vertex structures and are uniquely related to the four-color theorem in graph theory and the Potts model of statistical physics. Furthermore the phase transition into the ferromagnetic phase is associated with a variety of quantum phenomena, including Rashba superfluids, the Berezinskii-Kosterlitz-Thouless transition, and the Kibble-Zurek mechanism. Exploration of this quantum physics may have both academic and practical payoffs, including the development of a theoretical framework to understand quantum critical dynamics, simulations of N-pole ferromagnetic magnets, fabrication of programmable magnetic materials, and potentially even quantum information storage and processing.