Universality and Beyond in Atoms with Large Scattering Lengths

具有大散射长度的原子的普遍性和超越性

• 批准号: 1607190
• 负责人: Eric Braaten
• 金额: $ 27万
• 依托单位: Ohio State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-08-15 至 2020-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1607190&HistoricalAwards=false
• 关键词: Universality; Beyond; Atoms; Large; Scattering

The concept of reductionism in science refers to the general observation that physical characteristics of systems at the smallest length scale often determine macroscopic properties and phenomena. So copper wires and aluminum wires behave differently because of the physical characteristics of the atoms of which they are composed. Departures from reductionism are rare, but they do exist. This project explores a breakdown of reductionism known as "universality" that is sometimes displayed by ensembles of ultra-cold atoms. Ensembles of ultra-cold atoms provide especially important examples of universal phenomena because they can be controlled and probed with exquisite precision. They also provide valuable paradigms for universality in other fields of physics, including nuclear and particle physics, astrophysics, and condensed-matter physics. Examples of the universal properties observed in dilute, ultra-cold gases, independent of the species of atom employed, include the binding energies of weakly bound clusters, the reaction rates for collisions between atoms and clusters, and the stability or lifetime of trapped ensembles. This project will help to interpret these results, and to predict other observable, universal properties of ultra-cold systems. The goal of this research project is to extend our understanding of universal aspects of few-body and many-body systems consisting of atoms whose scattering length is large compared to the range of their interactions. The project has three major thrusts: (1) A recent breakthrough in calculating transition rates from an oscillating magnetic field near a Feshbach resonance will be applied to the breakup of paired fermions in a superfluid of fermionic atoms. The goal is to provide motivation for experiments that would make the first direct measurements of the pairing gap for superfluidity. (2) The first experiments on the unitary Bose gas, which consists of bosonic atoms with infinitely large scattering length, were carried out in the last few years. A new theoretical approach to the unitary Bose gas will be developed based on interpolating in the dimension of space (which is 3) using expansions around the critical dimensions 2 and 4, where the problem is simpler. (3) The simplest universal properties correspond to the mathematical limit in which the range of the interatomic potential is taken to zero and its strength is taken to infinity with the scattering length fixed. Additional universal aspects can be identified by expanding in powers of the range. Recent work simplifying the first-order range corrections for bosonic atoms will be extended and applied to results from cold atom experiments.

科学中的还原论概念是指一般的观察，即系统在最小长度尺度上的物理特性往往决定宏观性质和现象。因此，铜线和铝线的行为不同，这是因为组成它们的原子的物理特性。还原论的观点很少，但确实存在。这个项目探讨了一种被称为“普遍性”的还原论的崩溃，这种崩溃有时会通过超冷原子的集合来表现。超冷原子的集合提供了宇宙现象的特别重要的例子，因为它们可以被精确地控制和探测。它们也为其他物理学领域的普适性提供了有价值的范例，包括核和粒子物理学，天体物理学和凝聚态物理学。在稀释的超冷气体中观察到的普适性质的例子，与所使用的原子种类无关，包括弱结合簇的结合能，原子和簇之间碰撞的反应速率，以及被困系综的稳定性或寿命。该项目将有助于解释这些结果，并预测超冷系统的其他可观察的普遍性质。这个研究项目的目标是扩展我们对由原子组成的少体和多体系统的普遍方面的理解，这些原子的散射长度与它们的相互作用范围相比很大。该项目有三个主要目标：（1）最近从Feshbach共振附近的振荡磁场计算跃迁率的突破将应用于费米子原子超流体中成对费米子的分裂。目标是为实验提供动力，这些实验将首次直接测量超流性的配对间隙。(2)在过去的几年里，对由具有无限大散射长度的玻色原子组成的幺正玻色气体进行了第一次实验。一个新的理论方法，以酉玻色气体将开发的基础上，在空间的维度（这是3）使用扩展的临界尺寸2和4，其中的问题是简单的。(3)最简单的普适性质对应于数学极限，其中原子间势的范围取为零，其强度取为无穷大，散射长度固定。可以通过扩大范围的幂来确定其他的普遍方面。最近的工作简化玻色子原子的一阶射程修正将被扩展和应用到冷原子实验的结果。