Strongly Interacting Fermi Gases of Ultracold Atoms

超冷原子的强相互作用费米气体

• 批准号: 1506019
• 负责人: Martin Zwierlein
• 金额: $ 45万
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-08-15 至 2020-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1506019&HistoricalAwards=false
• 关键词: Strongly; Interacting; Fermi; Gases; Ultracold

Our modern world is run by electrons--they flow through our smart phones, computers, and machines to carry out a myriad of tasks from data storage and calculations to heavy lifting when employed in electromagnets. It is surprising that we do not better understand how electrons work together. This award supports studies of a novel substance, an ultracold gas of strongly interacting atoms, which behaves in many ways like electrons. For example, just like a metal becomes "superconducting" at low temperatures and starts to conduct electricity without resistance, the atomic gas becomes "superfluid" and atoms flow without friction. However, scaled to the density of electrons in metals, superfluidity would occur in the atomic gas already far above room temperature, thanks to the strong interatomic interactions. Just like electrons, but also protons and neutrons, the atoms belong to the class of particles called fermions, which cannot share one and the same state. This requirement makes computations extremely difficult and experiments indispensable to learn about the behavior of fermions. Confined in an artificial "box" of light, the atomic Fermi gas will be a pristine platform to learn about the equation of state of strongly interacting fermions, as they occur in modern materials, for example high-temperature superconductors, but also in neutron stars and nuclear matter. With the help of these and other studies, we might be led to an understanding on how to realize room temperature superconductivity. The project also holds the potential for observing new states of fermionic matter such as a supersolid--a superfluid that is also ordered like a crystal. The research will present a stimulating learning experience for graduate students.Ultracold Fermi gases of atoms represent a paradigmatic form of fermionic matter, where all details of the interparticle interaction, the external confinement, and the spin composition are precisely known and under the control of the experimenter. This project employs a Fermi gas of Lithium-6 atoms to try to answer long-standing questions about 1) the thermodynamics of two- and three-dimensional systems, 2) the fate of fermionic superfluidity in the presence of spin imbalance and 3) non-equilibrium dynamics in fermionic superfluids. The Fermi gas will be confined in tailored potentials, in particular a homogeneous box potential and a hybrid harmonic-box potential. Creating a homogeneous Fermi gas will take away many of the existing experimental limitations in obtaining accurate thermodynamic information. The box potential allows accessing new phases of fermionic matter that have not been observed before. The Berezinskii-Kosterlitz-Thouless superfluid in two dimensions features algebraic order that would be masked in an inhomogeneous trap. A homogeneous 3D Fermi superfluid in the presence of spin imbalance should spontaneously break translational symmetry by forming a train of solitons, where excess fermions reside in the nodes of the order parameter. This describes the famous Larkin-Ovchinnikov (LO) state, a supersolid phase of matter that has not been conclusively observed despite five decades of research. In the present work, soliton trains will be directly created in the presence of spin imbalance, thereby engineering the LO state.

我们的现代世界是由电子运行的-它们流过我们的智能手机，计算机和机器，以执行从数据存储和计算到电磁铁中使用的起重机的无数任务。令人惊讶的是，我们并没有更好地理解电子如何一起工作。该奖项支持对一种新物质的研究，这种物质是一种由强烈相互作用的原子组成的超冷气体，其行为在许多方面与电子相似。例如，就像金属在低温下变得“超导”并开始在没有电阻的情况下导电一样，原子气体变得“超流体”，原子在没有摩擦的情况下流动。然而，以金属中电子的密度来衡量，由于原子间的强相互作用，原子气体中的超流性将发生在已经远远高于室温的温度。就像电子，但也质子和中子，原子属于一类粒子称为费米子，它不能共享一个和相同的状态。这一要求使得计算变得极其困难，而要了解费米子的行为，实验是必不可少的。限制在一个人造的“盒子”的光，原子费米气体将是一个原始的平台，以了解强烈相互作用的费米子的状态方程，因为它们发生在现代材料，例如高温超导体，但也在中子星和核物质。在这些和其他研究的帮助下，我们可能会对如何实现室温超导性有所了解。该项目还具有观察费米物质新状态的潜力，例如超固体-一种也像晶体一样有序的超流体。这项研究将为研究生提供一个令人兴奋的学习体验。超冷费米原子气体代表了费米物质的一种典型形式，其中粒子间相互作用、外部约束和自旋组成的所有细节都是精确已知的，并在实验者的控制下。该项目采用锂-6原子的费米气体，试图回答长期存在的问题：1）二维和三维系统的热力学，2）自旋不平衡存在下费米超流的命运和3）费米超流中的非平衡动力学。费米气体将被限制在特制的势中，特别是均匀盒势和混合谐波盒势。创造一种均匀的费米气体将消除许多现有的实验限制，以获得准确的热力学信息。箱势允许访问以前没有观察到的费米子物质的新阶段。二维的Berezinskiii-Kosterlitz-无边界超流体具有代数序，这在非均匀陷阱中会被掩盖。一个均匀的三维费米超流体在自旋不平衡的存在下，应该自发地打破平移对称性，形成一系列的孤子，多余的费米子驻留在节点的序参数。这描述了著名的拉金-奥夫钦尼科夫（LO）态，这是一种物质的超固态，尽管经过了50年的研究，但尚未最终观察到。在目前的工作中，孤子序列将直接创建自旋不平衡的存在下，从而工程LO状态。