Quantum Gases of Bosonic and Fermionic Lithium

对于固体中的电子，众所周知，量子多体相互作用导致了材料的性质，如导电性和磁性。然而，对于气体中的原子来说，除非原子非常冷，否则很难观察到量子多体效应，因为热原子的行为更像是普通的弹道粒子。该项目将把锂原子冷却到开尔文的百万分之一度以下，并在光学陷阱中操纵超冷原子的气体，以研究量子力学如何影响大量原子。这将推动被称为量子多体物理的科学的发展。使用超冷原子的优点是它们的温度、密度和陷阱可以很容易地控制和调整。这一点很重要，因为它将帮助物理学家理解超导和奇异类型的磁性等现象。特别是，这个项目将研究磁学和超导电性如何共存。这将提高对高温超导体的基本理解，并可能制造出在更高温度下超导的新材料。该项目的另一部分将探索量子多体现象如何影响被称为孤子的集体波的传播。这个项目的这一部分很重要，因为它可以改进传感器。这个项目的两个部分都将使用锂的同位素，一个是玻色子，另一个是费米子。提出的玻色子实验的目标是探索近可积在明亮的物质波孤子中的作用，无论是基本孤子还是高阶孤子呼吸。该计划是使用由理论合作者开发的协议来创建呼吸器，并探索其与由蓝色失谐光片形成的分束器的相互作用。这些目标既有根本性的，也有技术性的。其中一个目标是创建一个介观(N=100-300)量子对象，并在一种新型的一维干涉仪中观察其性质，该干涉仪使用光片作为分束器。如果孤子的质心能量低于单个原子的结合能，它在与分束器相互作用时不会碎裂，而是整体隧穿和反射，从而产生薛定谔猫态。在这个项目的第二部分，这个实验室将实施新的想法，用自旋不平衡的费米气体创建和直接探测被称为FFLO(Fulde-Ferrell-Larkin-Ovchinnikov态)的奇异超导态。虽然FFLO在一维中普遍存在，但量子和热涨落都会破坏低维的长程有序。本实验室最近对自旋极化费米子气体中一维-三维交叉相图的测定指向了参数空间中FFLO既普遍又稳定的区域。这个团队的下一个目标是在一维的飞行时间扩展中检测未成对的费米子占据的周期性域壁。这将构成FFLO的第一个直接证据。

For electrons in solids it is well known that quantum many-body interactions cause material properties such as conductivity and magnetism. For atoms in a gas, however, it is difficult to observe quantum many-body effects unless the atoms are very cold, because hot atoms behave more like ordinary ballistic particles. This project will cool lithium atoms below one millionth of a degree Kelvin and manipulate gases of ultra-cold atoms in optical traps in order to study how quantum mechanics influences large collections of atoms. This will advance the science known as quantum many-body physics. The advantage of using ultra-cold atoms is that their temperature, density, and traps can be readily controlled and adjusted. This is important because it will help physicists understand phenomena such as superconductivity and exotic types of magnetism. In particular, this project will study how magnetism and superconductivity co-exist. This will improve the fundamental understanding of high-temperature superconductors, and may enable fabrication of new materials that superconduct at even higher temperatures. Another part of this project will probe how quantum many-body phenomena affect the propagation of collective waves known as solitons. This part of the project is important because it could lead to improved sensors.Both parts of this project will use an isotope of lithium, in one case a boson, while in the other a fermion. The goal of the proposed boson experiment is to explore the role of near-integrability in bright matter-wave solitons, either fundamental ones or higher-order soliton breathers. The plan is to create a breather using a protocol developed by theoretical collaborators, and to explore its interactions with a beam splitter formed from a blue-detuned light sheet. The goals are both fundamental and technological. One goal is to create a mesoscopic (N = 100-300) quantum object and observe its properties in a novel one-dimensional interferometer using the light sheet as a beam splitter. If the center-of-mass energy of the soliton is below the binding energy of a single atom, it will not fragment upon interacting with the beam splitter, but rather tunnel and reflect in its entirety, thus creating a Schrödinger cat state. In the second part of this project, this laboratory will implement new ideas for creating and directly detecting the exotic superconducting state known as FFLO (Fulde-Ferrell-Larkin-Ovchinnikov state) with a spin-imbalanced Fermi gas. While FFLO is prevalent in 1D, both quantum and thermal fluctuations tend to destroy long-range order in lower dimensions. The recent determination from this laboratory of the phase diagram of the 1D-3D dimensional crossover in a gas of spin-polarized fermions points to a region in parameter space where FFLO is both prevalent and stable. The next goal for this team is to detect the periodic domain walls occupied by the unpaired fermions in time-of-flight expansion in 1D. This would constitute the first direct evidence for FFLO.