Disordered Quantum Matter in Strongly Correlated Optical Lattices

强相关光学晶格中的无序量子物质

• 批准号: 1505468
• 负责人: Brian DeMarco
• 金额: $ 45万
• 依托单位: University of Illinois at Urbana-Champaign
• 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: 2015-09-01 至 2019-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1505468&HistoricalAwards=false
• 关键词: Disordered; Quantum; Matter; Strongly; Correlated

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.

这个项目的目的是提高无序如何影响电子固体的知识，如金属，绝缘体和超导体，构成现代技术的基础。 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有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通常是有害的，并且可以例如增加金属对电流的电阻。 另一方面，无序可能会增强超导性，即无电阻地传输电流，以及热电性，即将热量转化为电能。 一般来说，无序如何影响许多奇异的固体，如高温超导体，这可能会导致新的应用和更高的效率还不清楚。 在某种程度上，这种理解的缺乏是因为电子在这些材料中如何行为的最简单模型无法使用下一个世纪将创建的最强大的超级计算机来解决。 该项目将使用被困在光晶体中的原子，并将其冷却到绝对零度以上十亿分之一度，以在实验中模拟这些模型。 通过测量原子如何响应光和磁场的变化，将研究无序在金属、绝缘和超导状态之间转换固体的能力。 将探索使用无序作为新工具来抑制破坏信息存储等应用程序的过程的可能性。这些测量将被用来测试可能用于设计新材料的理论。无序对强关联电子固体（如高温超导体）行为的影响知之甚少，尽管这些材料中普遍存在缺陷。 数值模拟提供了有限的洞察力，理论一直受到挑战，以开发控制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，不精确的无序知识，以及诸如声子-电子散射的复杂性。 被困在光学晶格中的超冷K-40和Rb-87原子将用于探索Hubbard模型中无序对超流体的影响，Hubbard模型是强相关电子固体的最小模型。 在这些实验中，可控和精确表征的无序将引入使用光学散斑。 通过调节光学晶格势深度和经由Feshbach共振，将独立地操纵相互作用。 无序的吸引费米-哈伯德模型将首次使用原子通过调谐到Feshbach共振的吸引侧来实现。 输运和对分数测量的组合将被用来回答长期存在的问题，即费米子超流体如何在强关联系统中定位，即，无论是粒子对还是单个粒子构成了无序诱导的绝缘状态。 局部超流体中的再热化和弛豫（即，玻色玻璃）将通过测量准动量和密度分布来探测。 利用准动量选择性受激拉曼跃迁扰动原子的动量分布，并利用聚焦的蓝失谐激光束产生的局部排斥光学势控制密度分布。 测量结果将与最先进的理论和数值模拟进行比较。