Turbulence in quantum gases: setting the framework

量子气体中的湍流：设定框架

基本信息

批准号：
EP/I019413/1
负责人：
Carlo Barenghi
金额：
$ 43.14万
依托单位：
Newcastle University
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2012
资助国家：
英国
起止时间：
2012 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FI019413%2F1
关键词：
Turbulence quantum gases setting framework

项目摘要

At extremely low temperatures, matter behaves differently to what we are used to: its constituent particles are not independent but behave collectively as one entity, known as the Bose-Einstein Condensate (BEC). The condensate appears in solids, liquids, or gases, leading to some of the most fundamental physical phenomena. Historically the condensate has been studied extensively in liquid helium. At very low temperatures helium exhibits strange properties, which we can understand by describing helium as a combination of a usual liquid (the 'normal fluid') and a new 'quantum' liquid, called the 'superfluid', which can flow without the friction which a normal fluid would experience.Everybody is familiar with the jittery motion of an aeroplane due to the irregular motion of the turbulent air through which it flies. Turbulence is one of nature's most ubiquitous phenomenon: turbulent eddies and swirls occur in flows ranging from the aortic blood stream, to water and gas pipes, to winds in the atmosphere. Turbulence in superfluid helium has a new feature: it consists of discrete vortices, all with the same circulation and core structures, unlike the eddies of arbitrary shapes and strengths of ordinary fluids. This distinction arises because the superfluid consists of a condensate of many atoms, and is mathematically described by a single wavefunction: any rotational motion of the superfluid is constrained to vortices which are quantised, i.e. the flow around them is restricted by the laws of quantum mechanics.Recent experiments with superfluid helium have highlighted many remarkable similarities (e.g. energy spectra) and differences (e.g. velocity statistics) between ordinary turbulence and superfluid turbulence (also called quantum turbulence). Experimentalists have reported the existence of different regimes of quantum turbulence (e.g. random vs. structured), characterised by different temporal evolution (decay laws); theoreticians have proposed new mechanisms (e.g. the Kelvin wave cascade) for energy transfer and decay. The natural big question is whether ordinary turbulence is, in some sense, the classical limit of quantum turbulence: can the complexity of eddies and swirls in a turbulent stream be better understood in terms of the dynamics of a large number of discrete vortex filaments, each carrying one unit of circulation ?Parallel to this development, the last 15 years have seen the emergence of new physical systems for studying quantum effects on a macroscopic scale. Instead of working with liquid helium, whose constituent particles interact strongly, experimentalists have now created weakly-interacting trapped condensates of atoms in gases, known as quantum gases. Such systems provide an ideal context for the study of quantum turbulence, because they allow unprecedented experimental control of a vast range of parameters, such as the geometry and the effective dimensionality of the system, and the strength and the type of interactions (which can be tuned, rather than be given by nature as for helium). The first experimental evidence of turbulence in BEC ultracold gases was announced only last year. This proposal timely combines the above concepts in order to investigate turbulence in quantum gases. We think that, by promoting the study of more controllable atomic gases, the different forms of turbulence arising in classical and quantum systems can be better understood, particularly since quantum gases can be theoretically described very precisely. We plan to establish the framework for studying turbulence in atomic condensates, and address crucial questions in this new emerging field such as: how can we produce turbulence in a quantum gas in a controlled way ? what are the main features classifying the produced turbulent structure ? which experimental schemes are likely to produce the optimal results?

在极低的温度下，物质的行为与我们习惯的不同：其组成粒子不是独立的，而是作为一个实体共同表现，称为玻色-爱因斯坦凝聚体（BEC）。冷凝物以固体、液体或气体的形式出现，导致一些最基本的物理现象。历史上，人们对液氦中的凝析油进行了广泛的研究。在非常低的温度下，氦表现出奇怪的特性，我们可以通过将氦描述为普通液体（“正常流体”）和一种新的“量子”液体（称为“超流体”）的组合来理解这一点，这种液体可以在没有摩擦的情况下流动每个人都熟悉飞机由于飞行时湍流空气的不规则运动而产生的抖动。湍流是自然界中最普遍的现象之一：从主动脉血流到水和煤气管道，再到大气中的风，湍流涡流和漩涡都会发生。超流氦中的湍流有一个新特征：它由离散的涡流组成，所有涡流都具有相同的循环和核心结构，这与普通流体的任意形状和强度的涡流不同。出现这种区别是因为超流体由许多原子的凝聚体组成，并且在数学上由单个波函数描述：超流体的任何旋转运动都受到量子化的涡流的约束，即它们周围的流动受到量子力学定律的限制最近的超流氦实验强调了普通湍流和超流体之间的许多显着相似之处（例如能谱）和差异（例如速度统计）湍流（也称为量子湍流）。实验学家报告了不同状态的量子湍流的存在（例如随机与结构化），其特征是不同的时间演化（衰变定律）；理论家提出了能量转移和衰变的新机制（例如开尔文波级联）。自然的大问题是，在某种意义上，普通湍流是否是量子湍流的经典极限：湍流中涡流和漩涡的复杂性是否可以通过大量离散涡丝的动力学来更好地理解，每个涡丝携带一个循环单位？与这一发展并行的是，过去 15 年出现了用于研究宏观尺度量子效应的新物理系统。实验学家现在不再使用其组成粒子相互作用强烈的液氦，而是创造了气体中弱相互作用的原子俘获凝聚物，称为量子气体。这样的系统为量子湍流的研究提供了理想的背景，因为它们允许对大量参数进行前所未有的实验控制，例如系统的几何形状和有效维数，以及相互作用的强度和类型（可以是调整，而不是像氦一样由大自然赋予）。 BEC 超冷气体湍流的第一个实验证据去年才公布。该提案及时结合了上述概念，以研究量子气体中的湍流。我们认为，通过促进对更可控的原子气体的研究，可以更好地理解经典和量子系统中出现的不同形式的湍流，特别是因为量子气体可以在理论上非常精确地描述。我们计划建立研究原子凝聚态湍流的框架，并解决这个新兴领域的关键问题，例如：如何以受控方式在量子气体中产生湍流？对所产生的湍流结构进行分类的主要特征是什么？哪些实验方案可能产生最佳结果？