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Quantum vortex reconnections in trapped Bose-Einstein condensates

俘获玻色-爱因斯坦凝聚态中的量子涡旋重联

基本信息

批准号：
EP/R005192/1
负责人：
Carlo Barenghi
金额：
$ 47.72万
依托单位：
Newcastle University
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2017
资助国家：
英国
起止时间：
2017 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FR005192%2F1
关键词：
Quantum vortex reconnections trapped Bose

项目摘要

Long, almost one dimensional structures (filaments) are ubiquitous in the universe, consisting of chains of atoms (macromolecules) or regions of concentrated field lines (vortex lines in fluids, magnetic flux tubes in electrically conducting plasmas). Filaments occur at the microscopic scale of proteins and DNA, through the intermediate scales of tornadoes, dust devils and the trails behind planes and boats, up to the huge scales of the star-forming clouds in outer space. When two filaments come close to each other, they can split and recombine, having exchanged strands. Such reconnection events not only change the geometry of the filaments themselves but they also change the underlying topology (the property for which two rings which are linked to each other are different from two rings which are separated). A better understanding of reconnections is therefore crucial to many problems in the natural sciences and in engineering (for example, how the energy of a fluid is spread by reconnections). With reconnections arising across many distinct physical contexts and over many scales, it is natural to ask whether any behaviours are universal, such that a shared framework of understanding can be sought. For example, the loss of energy during a reconnection in a fluid is directly analogous to that which occurs during a reconnection in a plasma despite different physical origins of the loss of energy (viscosity in the fluid and electrical resistivity in the plasma). Other examples debated in the scientific community are whether a measure of the coiling, twisting and linking of the filaments, termed the helicity, is conserved during reconnections, and whether complicated tangled knots of filaments may decay or disentangle in ways which depend on the topology rather than the physical nature of the system. Our understanding of reconnections is still in its infancy and would benefit from detailed quantitative measurements of reconnections, and from comparison of reconnections across different scientific disciplines.In this context, trapped atomic Bose-Einstein condensates (BECs) provide an ideal testing ground to study reconnections. BECs are gases of atoms, cooled to within a few billionths of a degree above absolute zero. Here the blurry laws of quantum mechanics rule and transform the gas into a quantum fluid. This type of fluid is remarkable in its simplicity: while everyday fluids possess viscosity and can form tornadoes of any size or shape, quantum fluids have no viscosity and their tornadoes have a fixed size and shape. This makes them easier to conceptualise, model and understand. What is more, experimentalists are able to control and manipulate the fluid, and its vortices, to a high level of precision. Our recent preliminary work in collaboration with an experimental group in Trento, Italy, not only demonstrated reconnections in BECs for the first time, but also revealed new and unexpected forms of reconnections. Motivated by this, we will perform detailed computer simulations of vortex reconnections in the ideal context provided by BECs, determining exactly how reconnections occur and what their consequences are. Then, by comparing to the behaviour in different settings (ordinary fluids, plasmas and macromolecules) we will probe whether universal behaviours do exist (for example, if the distance between reconnecting strands scales with time with a universal power law, or if energy losses relate to the amount of knottedness), probing the relation between energy and topology in different systems. To disseminate our results across scientific communities, we will organise an interdisciplinary workshop on reconnections with the top experts from atomic physics, astrophysics, fluid dynamics, knot theory, with a view to building a common picture. Close collaboration with the ongoing experiment at Trento will guide our theoretical studies and provide immediate experimental tests of our findings.

长的，几乎是一维的结构（细丝）在宇宙中无处不在，由原子链（大分子）或集中场线的区域（流体中的涡线，导电等离子体中的磁通管）组成。丝状体出现在蛋白质和DNA的微观尺度上，穿过龙卷风、尘暴和飞机和船只后面的痕迹的中等尺度，直到外层空间恒星形成云的巨大尺度。当两个细丝彼此靠近时，它们可以分裂和重组，交换股。这种重连事件不仅改变了细丝本身的几何形状，而且还改变了底层的拓扑结构（两个相互连接的环与两个分开的环不同的性质）。因此，更好地理解重连对自然科学和工程学中的许多问题至关重要（例如，流体的能量如何通过重连传播）。随着在许多不同的物理环境和许多尺度上出现的重新连接，人们很自然地会问，是否有任何行为是普遍的，这样就可以寻求一个共同的理解框架。例如，在流体中重连期间的能量损失直接类似于在等离子体中重连期间发生的能量损失，尽管能量损失的物理来源不同（流体中的粘度和等离子体中的电阻率）。科学界争论的其他例子是，在重连过程中，细丝的卷曲、扭曲和连接（称为螺旋度）是否保持不变，以及复杂的细丝缠结结是否会以依赖于拓扑结构而不是系统的物理性质的方式衰变或解开。我们对重连的理解仍处于起步阶段，如果能对重连进行详细的定量测量，并对不同学科的重连进行比较，将有助于我们对重连的理解。在这种情况下，囚禁原子玻色-爱因斯坦凝聚（BEC）为研究重连提供了一个理想的实验平台。BEC是原子气体，冷却到绝对零度以上几十亿分之一度。在这里，量子力学的模糊定律支配并将气体转化为量子流体。这种类型的流体在其简单性方面是显着的：虽然日常流体具有粘性，可以形成任何大小或形状的龙卷风，但量子流体没有粘性，它们的龙卷风具有固定的大小和形状。这使得它们更容易概念化，建模和理解。更重要的是，实验者能够控制和操纵流体及其漩涡，达到高精度。我们最近与意大利特伦托的一个实验小组合作的初步工作，不仅首次证明了BEC中的重连，而且还揭示了新的和意想不到的重连形式。受此启发，我们将在BEC提供的理想环境中对涡旋重连进行详细的计算机模拟，确定重连是如何发生的以及它们的后果是什么。然后，通过比较不同环境（普通流体，等离子体和大分子）中的行为，我们将探索是否存在普遍的行为（例如，如果重新连接的链之间的距离与时间成比例与普遍的幂律，或者如果能量损失与打结的数量有关），探索不同系统中能量和拓扑结构之间的关系。为了在科学界传播我们的成果，我们将组织一个跨学科研讨会，与原子物理学，天体物理学，流体动力学，纽结理论的顶级专家重新联系，以期建立一个共同的图景。与特伦托正在进行的实验的密切合作将指导我们的理论研究，并为我们的发现提供直接的实验测试。