Theoretical Studies of Dilute Alkali Gases and Amorphous Materials

这项拨款解决了凝聚态物理新兴领域中两个具有挑战性的问题的理论问题：稀碱玻色和费米气体的性质以及非晶材料的“普遍”性质。在第一个领域，解决了几个问题：(a)最近发现的一种状态的行为，在这种状态中，不是一个，而是两个轨道单粒子态被宏观占据；(b)从ramsey条纹型实验推断玻色-爱因斯坦凝聚度（BEC）的条件；(c)当光学屏障降低或移除时，在“莫特绝缘体”状态下被困在光学晶格中的玻色气体转变为超流体（相参）状态的过程的详细动力学；(d)稀释玻色气体在s波散射长度趋于无穷大时的行为；(e)在具有吸引的种间相互作用的稀两种费米碱-气体体系中，在向BCS态的转变温度和/或配对振幅上可能存在限制。第二个主要推动力在本质上更具投机性；人们正试图定量地实现几年前提出的一个关于非晶材料（玻璃）的“普遍”行为的建议，即这种行为与这些材料中普遍存在的“隧道-两能级系统”无关。这是目前建立的模型所要求的，但更确切地说，这是在短长度尺度上存在的任何一种非谐波激励的一个相当普遍的结果，这些激励可以由弹性介质耦合。除了这两个主要的项目，在非常简并费米系统的猝灭和铜超导方面的工作正在进行中。提议的项目是现代凝聚态物理的智力核心，成功将具有根本性的影响。同样，这项研究的成功完成将影响许多其他领域的研究。学生们将接受培训，首席研究员也正在为研究生编写一本关于量子液体的教科书。该基金解决了凝聚态物理学新兴领域中两个具有挑战性问题的理论问题，凝聚态物理学是研究固体或液体物质的物理学分支。第一个领域是对稀的、超冷的气体的特性的理论研究，这些气体会凝结成一个独特的量子相。这一独特相位的发现，在许多年前就被预测出来了，最近获得了诺贝尔奖。还有很多研究要做。第二个研究领域是非晶材料（玻璃）奇怪而“普遍”的行为。在非常低的温度下，不同的材料表现出共同的性质，表明一种共同的机制。我们将探讨这些共同属性的可能模型。提议的项目是现代凝聚态物理的智力核心，成功将具有根本性的影响。同样，这项研究的成功完成将影响许多其他领域的研究。学生们将接受培训，首席研究员也正在为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.***