Disordered Quantum Matter in Strongly Correlated Optical Lattices

该项目的目的是提高对无序如何影响电子固体的认识，如金属、绝缘体和超导体，它们构成了现代技术的基础。控制电子在固体中如何携带热量、能量和信息的能力使诸如计算机和高效能源产生和传输等应用成为可能。固体中固有的无序和缺陷通常是有害的，例如，会增加金属对电流的电阻。另一方面，无序可能会增强超导性（无电阻传输电流）和热电性（将热量转化为电能）。一般来说，无序如何影响许多外来固体，如高温超导体，这可能导致新的应用和更高的效率尚不清楚。在某种程度上，这种缺乏理解的原因是，即使是下个世纪即将问世的最强大的超级计算机，也无法解决电子在这些材料中的行为的最简单模型。这个项目将使用被困在光晶体中的原子，并将其冷却到比绝对零度高十亿分之一度的温度，在实验中模拟这些模型。通过测量原子对光和磁场变化的反应，将研究无序在金属态、绝缘态和超导态之间转变固体的能力。将探索使用无序作为一种新工具来抑制破坏信息存储等应用程序的过程的可能性。这些测量结果将被用来检验设计新材料的理论。尽管在这些材料中普遍存在缺陷，但无序对强相关电子固体（如高温超导体）行为的影响知之甚少。数值模拟提供了有限的见解，理论已经受到挑战，以发展控制的方法来理解强相互作用和无序的相互作用。此外，由于无法单独控制材料参数，对无序的不精确认识以及诸如声子电子散射等复杂性，使用材料测量来测试理论和模拟变得复杂。超冷K-40和Rb-87原子被困在光学晶格中，将用于探索无序对Hubbard模型中超流体的影响，该模型是强相关电子固体的最小模型。在这些实验中，将使用光学散斑引入可控制和精确表征的无序。相互作用将通过调整光学晶格势深度和费什巴赫共振来独立操纵。无序吸引费米-哈伯德模型将首次通过调整到费什巴赫共振的吸引侧来实现。输运和对分数测量的结合将用于回答长期存在的费米子超流体如何在强相关系统中局部化的问题，即，是对粒子还是单个粒子构成了无序诱导的绝缘状态。局域超流体（即玻色玻璃）中的再热化和弛豫将通过准动量和密度剖面的测量来探测。原子动量分布将使用准动量选择性受激拉曼跃迁来干扰平衡，密度分布将使用聚焦蓝失谐激光束产生的局部排斥光势来操纵。测量结果将与最先进的理论和数值模拟进行比较。

The purpose of this project is to enhance knowledge of how disorder affects the electronic solids, such as metals, insulators, and superconductors, that form the basis of modern technology. The ability to control how electrons carry heat, energy, and information in solids enables applications such as computers and efficient energy generation and transmission. The disorder and imperfections inherent in solids are often deleterious and can, for example, increase the resistance of metals to electrical current flow. On the other hand, disorder may enhance superconductivity, which is transmitting electrical current without resistance, and thermoelectricity, which is transforming heat into electrical energy. In general, how disorder affects many exotic solids, such as high-temperature superconductors, that may lead to new applications and higher efficiencies is not understood. In part, this lack of understanding arises because the simplest models of how electrons behave in these materials cannot be solved using even the most powerful supercomputers that will be created over the next century. This project will use atoms trapped in a crystal of light and cooled to just a billionth of a degree above absolute zero temperature to simulate these models in an experiment. The ability of disorder to transform solids between metallic, insulating, and superconducting states will be investigated by measuring how the atoms respond to changes in the light and magnetic fields. The possibility to use disorder as a new tool to suppress processes that disrupt applications such as information storage will be explored. These measurements will be employed to test theories that may be used to design novel materials. The influence of disorder on the behavior of strongly correlated electronic solids, such as high-temperature superconductors, is poorly understood, despite the prevalence of imperfections in these materials. Numerical simulations provide limited insight, and theory has been challenged to develop controlled approaches to understanding the interplay of strong interactions and disorder. Furthermore, using measurements on materials to test theory and simulations is complicated by the inability to separately control material parameters, imprecise knowledge of disorder, and complications such as phonon-electron scattering. Ultracold K-40 and Rb-87 atoms trapped in optical lattices will be used to explore the impact of disorder on superfluids in Hubbard models, which are minimal models of strongly correlated electronic solids. In these experiments, controllable and precisely characterized disorder will be introduced using optical speckle. The interactions will be manipulated independently by tuning the optical lattice potential depth and via a Feshbach resonance. The disordered attractive Fermi-Hubbard model will be realized for the first time using atoms by tuning to the attractive side of a Feshbach resonance. Combinations of transport and pair fraction measurements will be employed to answer the long-standing question of how fermionic superfluids localize in strongly correlated systems, i.e., whether pairs or single particles constitute the disorder-induced insulating state. Rethermalization and relaxation in localized superfluids (i.e., Bose-glasses) will be probed by measurements of quasimomentum and density profiles. The atomic momentum distribution will be disturbed from equilibrium using quasi-momentum-selective stimulated Raman transitions, and the density profile will be manipulated using a local, repulsive optical potential created by a focused blue-detuned laser beam. Measurements will be compared with state-of-the-art theory and numerical simulations.