权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Ultracold Gases far from Equilibrium: Fluctuations in time-dependent Geometries

远离平衡的超冷气体：随时间变化的几何形状

基本信息

批准号：
EP/F055935/1
负责人：
Nikolaos Proukakis
金额：
$ 32.63万
依托单位：
Newcastle University
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2009
资助国家：
英国
起止时间：
2009 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FF055935%2F1
关键词：
Ultracold Gases far Equilibrium Fluctuations

项目摘要

Intensive research over the last 15 years has shown that one can cool atoms in a gas by suitable use of magnets and light to a tiny fraction above absolute zero, the temperature at which all motion freezes. At such a low temperature, atoms suddenly experience an 'identity crisis', and are coerced into behaving identically - what is scientifically termed 'coherently'. Because these 'ultracold' atoms are almost stationary, they can actually become sensitive 'measuring devices' of effects they would otherwise essentially not feel, such as gravity, or magnetic fields. Suitable devices have been constructed to take advantage of this, and are known as 'atom interferometers'. In such devices, a group of trapped, very cold atoms is split into two smaller groups of approximately equal size in physically-separated locations, and then subsequently joined together again. A study of the properties of the atoms after they are joined reveals important information about changes in phenomena taking place when they were separated (e.g. changes in the strength of gravity between the two separated locations). Such a 'measuring device' has essentially two variants, depending on whether the atoms were originally stationary or moving, with each scheme having its own benefits and shortcomings. In order to take full advantage of such devices, one should develop a detailed understanding of the physical processes that take place in such systems, and this project intends to make significant advances in this area.A detailed description of such systems is complicated by the fact that at the typical temperatures where most current experiments take place, only some of the atoms behave 'coherently', with the rest of the atoms behaving in a random fashion, just like atoms in the air around us. Moreover, our ability to control the motion of atoms appears to be enhanced in thin long geometries, but this significant benefit is partly counterbalanced by the tendency of such geometries to destroy the 'coherent' nature of the system; the latter is due to fluctuations (in the phase of the system) which arise as a fundamental consequence of quantum mechanics, the theory which describes the microscopic world. Any theoretical model attempting to describe such experiments accurately should take account of these issues.The main aims of this project are two-fold: (i) firstly, to perform an in-depth study of fundamental physical mechanisms which may restrict the accuracy of such devices. (ii) Secondly, this project addresses the crucial question of how feasible it is to produce in a controlled manner a beam of atoms which maintain their coherence, even though they are actually moving, a topic of great current interest. Although there are numerous related theoretical studies in the literature, this work is unique in that it combines essential features that have to date only been implemented in independent studies: (i) firstly, this study is performed under realistic conditions, in which only some of the atoms behave coherently, and includes the full dynamics of both 'coherent' and 'random' atoms and their interactions. (ii) Moreover, additional complications (phase fluctuations) arising from the fact that these systems are very thin and long are also treated by advanced (stochastic) techniques, which are naturally 'built into' the approach mentioned above, with such a generalised theory solved numerically for the first time in the present work.Motivated by recent pioneering experiments which remain only partly understood, we use computers to study how the properties of the atoms are affected upon changing various parameters of the system, such as geometry, size and temperature, and we further investigate related issues in moving atoms.

过去15年的深入研究表明，人们可以通过适当地使用磁铁和光，将气体中的原子冷却到比绝对零度（所有运动都冻结的温度）略高的一点。在如此低的温度下，原子突然经历了一场“身份危机”，并被迫表现出相同的行为——这在科学上被称为“相干”。因为这些“超冷”原子几乎是静止不动的，它们实际上可以成为敏感的“测量设备”，测量它们本来根本感受不到的效应，比如重力或磁场。为了利用这一点，人们已经构造了合适的设备，称为“原子干涉仪”。在这种装置中，一组被困住的非常冷的原子在物理上分开的位置被分成两个大小大致相等的小原子，然后又重新结合在一起。对原子结合后的性质的研究揭示了它们分离时发生的现象变化的重要信息（例如，两个分离位置之间重力强度的变化）。这种“测量装置”本质上有两种变体，取决于原子最初是静止的还是运动的，每种方案都有自己的优点和缺点。为了充分利用这些设备，人们应该对这些系统中发生的物理过程有一个详细的了解，这个项目打算在这个领域取得重大进展。在当前大多数实验进行的典型温度下，只有一些原子的行为是“相干的”，其余的原子的行为是随机的，就像我们周围空气中的原子一样，这使得对这种系统的详细描述变得复杂。此外，我们控制原子运动的能力似乎在细长的几何形状中得到了增强，但这种显著的好处在一定程度上被这种几何形状破坏系统的“相干”性质的趋势所抵消；后者是由于（系统的相位）波动引起的，这是量子力学的一个基本结果，量子力学是描述微观世界的理论。任何试图准确描述这类实验的理论模型都应该考虑到这些问题。该项目的主要目的有两个方面：(i)首先，对可能限制此类设备准确性的基本物理机制进行深入研究。第二，这个项目解决了一个关键问题，即以一种受控的方式产生一束原子，即使它们实际上在运动，也能保持它们的相干性，这是目前非常感兴趣的一个问题。虽然文献中有许多相关的理论研究，但这项工作的独特之处在于它结合了迄今为止仅在独立研究中实现的基本特征：(i)首先，本研究是在现实条件下进行的，其中只有一些原子的行为是连贯的，并且包括“连贯”和“随机”原子及其相互作用的完整动力学。（ii）此外，由于这些系统很薄很长而引起的额外的复杂性（相位波动）也可以用先进的（随机）技术来处理，这些技术自然地“内置”在上述方法中，在本工作中第一次用数值方法解决了这样一个广义理论。受最近的开创性实验的启发，我们使用计算机来研究改变系统的各种参数（如几何形状、大小和温度）如何影响原子的性质，并进一步研究运动原子的相关问题。

项目成果

期刊论文数量（10）

专著数量（0）

科研奖励数量（0）

会议论文数量（0）

专利数量（0）

Ab initio modelling of quasi-one-dimensional Bose gas experiments via the stochastic Gross-Pitaevskii equation

通过随机 Gross-Pitaevskii 方程对准一维玻色气体实验进行从头建模

DOI：
发表时间：
2013
期刊：
影响因子：
0
作者：
Gallucci Donatello
通讯作者：
Gallucci Donatello

Evaporative cooling of cold atoms at surfaces

DOI：
10.1103/physreva.90.023614
发表时间：
2014-05
期刊：
Physical Review A
影响因子：
2.9
作者：
J. Markle;A. J. Allen;P. Federsel;B. Jetter;A. Gunther;J. Fort'agh;N. Proukakis;T. Judd
通讯作者：
J. Markle;A. J. Allen;P. Federsel;B. Jetter;A. Gunther;J. Fort'agh;N. Proukakis;T. Judd

Cross-over to quasi-condensation: mean-field theories and beyond