OP: Quantum Phases and Dynamics of Bose-Einstein Condensates with Artificial Gauge Fields

该项目研究现代物理学的基石之一量子力学预测的基本自然定律。与日常生活的经验相比，量子力学的预测是非常违反直觉和不熟悉的，但当空间维度变小时，它们起着主导作用，例如在使用现代纳米纤维或计算机芯片制造技术达到的长度尺度上，以及在原子尺度上。在纳米尺度上进行实验存在严重的技术困难，但存在另一种方法：当原子气体冷却到接近绝对零度时，也可以研究量子力学的相同定律。在这些温度下，基本量子长度变得更大，这些超冷量子气体的细节可以在定制的显微镜中成像，允许使用原子物理学领域的工具以非常灵活的方式检查它们的性质。在这个项目中研究的特定预测涉及一种称为自旋轨道耦合的性质。在绝大多数现有的电子器件中，带电粒子（即，电子）用于执行器件功能。然而，电子有一个额外的属性，称为自旋，它可以被描绘成一个快速旋转的运动，类似于旋转的陀螺。这种旋转的方向也可以用来执行设备功能，导致“自旋电子”设备。自旋-轨道耦合表示这种自旋运动与构成常规电流的粒子线性流动之间的相互作用。它是许多未来设备和具有奇异特性的先进材料的基本组成部分。基本物理相当复杂，该项目的实验为探索新概念提供了重要的试验平台。 近年来，将超冷原子浸入合适的激光束中已经成为研究量子动力学的有力工具。由激光耦合的不同超精细态可以被认为是“伪”自旋的取向，因此光子的吸收和发射构成自旋翻转。同时，由于动量守恒，当光子被吸收或发射时，原子的运动会发生变化。结果，原子的赝自旋和运动在激光驱动的跃迁中耦合，类似于凝聚态物理学中已知的自旋-轨道耦合。用激光对原子进行适当的修饰也可以产生人工规范场和人工磁场和电场，因此带电粒子的行为可以用中性原子量子气体来研究。此外，原子的色散关系可以被修改，以表现出有趣的双阱结构，显示出类Roton极小值。 在过去的资助期间，这种技术已被应用到铷玻色-爱因斯坦凝聚体，以研究量子相位和自旋轨道耦合凝聚体的量子动力学。 利用上一个资助期获得的见解和技术发展，该项目将探索挑战当前理论描述的新领域。方面包括新的量子相位诱导的自旋-轨道耦合和与光晶格的相互作用，以及孤子在自旋-轨道耦合的环境和拓扑结构在更高的维度的动力学。

This project investigates fundamental laws of nature predicted by quantum mechanics, one of the cornerstones of modern physics. The predictions of quantum mechanics are very counterintuitive and unfamiliar compared to the experiences of everyday life, but they play a dominant role when spatial dimensions get small, e.g. at length scales reached using modern nanofabrication or computer chip fabrication techniques, and on atomic scales. Conducting experiments on the nanoscopic length scale poses severe technical difficulties, but an alternative approach exists: the same laws of quantum mechanics can also be studied when a gas of atoms is cooled down to temperatures near absolute zero. At these temperatures, fundamental quantum lengths become larger and details about these ultracold quantum gases can be imaged in a custom microscope, allowing their properties to be examined in very flexible ways using tools from the realm of atomic physics. The particular predictions investigated in this project concern a property called spin-orbit coupling. In the vast majority of existing electronic devices, the transport of electrically charged particles (i.e., electrons) is exploited to perform a device function. However, electrons have an additional property called spin, which can be pictured as a fast spinning motion akin to that of a spinning top. The orientation of this rotation can also be used to perform a device function, leading to "spintronic" devices. Spin-orbit coupling denotes an interplay between this spinning motion and the linear flow of particles that constitutes a conventional current. It is the basic building block of many proposed future devices and of advanced materials with exotic properties. The underlying physics are rather complex, and the experiments of this project provide an important test bed with which new concepts are explored. Over the recent years, immersing ultracold atoms into suitably tailored laser beams has emerged as a powerful tool to investigate quantum dynamics. The different hyperfine states coupled by the lasers can be considered orientations of a "pseudo" spin, so that absorption and emission of a photon constitutes a spin flip. At the same time, due to momentum conservation, the atom's motion is changed when a photon is absorbed or emitted. As a result, the pseudospin and the motion of an atom become coupled in a laser-driven transition, in analogy to spin-orbit coupling known from condensed matter physics. A suitable dressing of atoms with laser light can also lead to artificial gauge fields and artificial magnetic and electric fields, so that charged-particle behavior can be investigated with neutral atomic quantum gases. Furthermore, the dispersion relation of the atoms can be modified to exhibit intriguing double-well structures showing roton-like minima. Over the previous grant period, such techniques have been applied to a rubidium Bose-Einstein condensate to investigate quantum phases and quantum dynamics in spin-orbit coupled condensates. Capitalizing on the insights gained and technological developments performed in the previous grant period, this project will explore new frontiers that challenge current theoretical descriptions. Aspects include novel quantum phases induced by spin-orbit coupling and by the interplay with optical lattices, as well as the dynamics of solitons in a spin-orbit coupled environment and topological structures in higher dimensions.