Disordered Quantum Matter in Strongly Correlated Optical Lattices

这个项目的目的是加强对无序如何影响构成现代技术基础的电子固体，如金属、绝缘体和超导体的知识。控制电子如何在固体中携带热量、能量和信息的能力使计算机和高效的能量产生和传输等应用成为可能。固体中固有的无序和缺陷往往是有害的，例如，会增加金属对电流流动的阻力。另一方面，无序可能会增强超导电性和热电性，前者是在没有电阻的情况下传输电流，后者是将热能转化为电能。一般来说，无序如何影响许多奇异的固体，例如高温超导体，可能导致新的应用和更高的效率，目前还不清楚。在一定程度上，这种缺乏理解的原因是，即使是最简单的电子在这些材料中行为的模型，也无法使用下个世纪将创造的最强大的超级计算机来解决。该项目将使用捕获在光晶体中的原子，并将其冷却到仅比绝对零度高十亿分之一度的温度，以在实验中模拟这些模型。通过测量原子对光场和磁场变化的反应，将研究无序在金属、绝缘和超导状态之间转换固体的能力。将探索将无序作为一种新工具来抑制扰乱信息存储等应用程序的过程的可能性。这些测量将被用来测试可能被用来设计新材料的理论。无序对高温超导体等强关联电子固体行为的影响，尽管这些材料中普遍存在缺陷，但人们对此知之甚少。数值模拟提供的洞察力有限，理论受到挑战，无法开发可控的方法来理解强相互作用和无序的相互作用。此外，使用材料测量来测试理论和模拟是复杂的，因为无法单独控制材料参数，对无序的不精确知识，以及声子-电子散射等复杂情况。利用捕获在光学晶格中的超冷K-40和RB-87原子来探索无序对Hubbard模型中超流体的影响，Hubbard模型是强关联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和精确表征的无序。这些相互作用将通过调节光学晶格势深度和费什巴赫共振独立地进行操作。无序吸引费米-哈伯德模型将首次利用原子通过调谐到费什巴赫共振的吸引端来实现。输运和对分数测量的结合将被用来回答一个长期存在的问题，即费米子超流体如何在强关联系统中定域，即是双粒子还是单粒子构成无序诱导的绝缘态。定域超流体(即玻色玻璃)中的再热化和弛豫将通过测量准分子和密度分布来探讨。原子的动量分布将通过准动量选择的受激拉曼跃迁被扰乱，而密度分布将被利用由聚焦的蓝失谐激光产生的局域排斥光势来操纵。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.