Theoretical Studies of Dilute Alkali Gases and Amorphous Materials

这项研究解决了凝聚态物理学新兴领域中两个具有挑战性的理论问题：稀碱玻色气体和费米气体的性质以及非晶态材料的“普适”性质。在第一个领域中，讨论了几个问题：(A)最近发现的一个态的行为，在这个态中，宏观上占据了不是一个而是两个轨道单粒子态；(B)从Ramsey条纹型实验中可以推断玻色-爱因斯坦凝聚(BEC)的程度的条件；(C)当光学势垒降低或移除时，囚禁在光学晶格中的玻色气体转变为超流体(相干态)的详细动力学过程；(D)在S波散射长度趋于无穷大的极限下，稀薄玻色气体的行为；(E)在具有吸引的物种间相互作用的稀释费米碱-气体系统中，对转变到BCS态的温度和/或对振幅的可能极限。第二大推力本质上更具投机性；正试图定量地实施几年前提出的关于非晶态材料(玻璃)的“普遍”行为的提议，即该行为与当前建立的模型所要求的在这些材料中普遍存在的“隧穿-二能级系统”无关，而是在短长度尺度上存在任何类型的非简谐且可由弹性介质耦合的激发的相当一般的结果。除了这两个主要项目之外，关于非常简并费米系统的猝灭和铜酸盐超导体的工作正在进行中。拟议的项目是现代凝聚态物理的智力核心，成功将是根本的结果。同样，这项研究的成功完成将影响到许多其他研究领域。学生将接受培训，首席研究人员还将为初学研究生编写一本关于量子液体的教科书。这笔拨款解决了凝聚态物理学新兴领域中两个具有挑战性的问题的理论问题。凝聚态物理学是物理学的一个分支，研究固体或液体中的物质。第一个领域是对凝聚成独特量子相的稀薄、超冷气体性质的理论研究。多年前预测的这一独特阶段的发现，最近赢得了诺贝尔奖。还有很多研究要做。第二个研究领域是非晶态材料(玻璃)的奇怪和“普遍”行为。在非常低的温度下，不同的材料表现出共同的性质，这表明了共同的机制。我们将探索这些共同性质的可能模型。拟议中的项目是现代凝聚态物理学的智力核心，成功将是根本的结果。同样，这项研究的成功完成将影响到许多其他研究领域。学生将接受培训，首席研究员还将为初级研究生编写一本关于量子液体的教科书。*

This grant addresses theoretical questions in two challenging problems in emerging areas in condensed matter physics: properties of dilute alkali Bose and Fermi gases and the "universal" properties of amorphous materials.In the first area, several questions are addressed: (a) the behavior of a recently discovered state in which not one, but two, orbital single-particle states are macroscopically occupied; (b) the conditions under which the degree of Bose-Einstein condensation (BEC) may be inferred from Ramsey-fringe type experiments; (c) the detailed dynamics of the process by which a Bose gas trapped in an optical lattice in a "Mott-insulator" state converts into a superfluid (phase-coherent) state when the optical barriers are lowered or removed; (d) the behavior of a dilute Bose gas in the limit that the s-wave scattering length tends to infinity; (e) in a dilute two-species Fermi alkali-gas system having attractive inter-species interactions, to possible limits on the transition temperature to the BCS state, and/or on the pairing amplitudes.The second major thrust is more speculative in nature; an attempt is being made to implement quantitatively a proposal made several years ago concerning the "universal" behavior of amorphous materials (glasses), namely that this behavior has nothing to do with the ubiquitous presence in these materials of "tunneling-two-level systems," which is required by the currently established model, but rather is a quite generic consequence of the presence at short length scales of any kind of excitations that are not harmonic and that can be coupled by the elastic medium.In addition to these major two projects, work is ongoing on quenching in very degenerate Fermi systems and on cuprate superconductivity.The proposed projects are at the intellectual core of modern condensed matter physics and success will be of fundamental consequence. Likewise, successful completion of this research will affect many other fields of study. Students will be trained and the principal investigator is also writing a textbook on quantum liquids for beginning graduate students.%%%This grant addresses theoretical questions in two challenging problems in emerging areas in condensed matter physics - that branch of physics that deals with matter in its solid or liquid phases. The first area is theoretical studies of the properties of dilute, ultra-cold gases that condense into a unique quantum phase. Discovery of this unique phase, predicted many years ago, has earned recent Nobel Prizes. Much research has yet to be done. The second research area is the strange and "universal" behavior of amorphous materials (glasses). At very low temperatures diverse materials exhibit common properties indicating a common mechanism. A possible model for these common properties will be explored.The proposed projects are at the intellectual core of modern condensed matter physics and success will be of fundamental consequence. Likewise, successful completion of this research will affect many other fields of study. Students will be trained and the principal investigator is also writing a textbook on quantum liquids for beginning graduate students.***