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Dilute Quantum Fluids Beyond the Mean-Field

超出平均场的稀释量子流体

基本信息

批准号：
EP/T015241/1
负责人：
Simon Cornish
金额：
$ 102.6万
依托单位：
Durham University
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2020
资助国家：
英国
起止时间：
2020 至无数据
项目状态：
未结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FT015241%2F1
关键词：
Dilute Quantum Fluids Beyond Mean

项目摘要

If we peer deep inside nature to a microscopic level, we find a strange world governed by quantum mechanics where our intuition breaks down. In this fascinating regime, the position of a particle has inherent uncertainty and is perpetually fluctuating. Such quantum fluctuations lie at the heart of a number of physical phenomena, ranging from the van der Waals force to Hawking radiation in black holes, and may provide the ultimate limit to technologies based on quantum effects. However, quantum fluctuations are difficult to observe experimentally and to describe theoretically.Since their realization in 1995, Bose-Einstein condensates (BECs) have provided a unique window through which to view the quantum world. A BEC is a gas of identical atoms cooled down to less than a millionth of a degree above absolute zero. At this point the uncertainty in an individual atom's position becomes greater than the separation between atoms and it is impossible to identify individual atoms. Instead, the gas behaves like a giant wave of matter dominated by quantum mechanics, and displays a range of striking quantum properties such as the ability to interfere with another BEC and the ability to flow without viscosity (superfluidity). In addition, BECs are amenable to a high degree of experimental control (for example, to manipulate and interrogate the system in time and space) and they can be imaged to high resolution. The behaviour of BECs, including the properties above, are captured to a high degree of accuracy by considering just the average behaviour of all the atoms: the so-called "mean-field". Over the years since 1995, a synergy of experiments and theoretical works have established a deep understanding of the quantum mean-field and how it influences the system behaviour. However, in a BEC, quantum fluctuations are small compared to the mean-field, and as such, the merits offered by BECs have not extended to the realm of quantum fluctuations.Enter the quantum liquid droplet. When two BECs co-exist, the mean-field quantum effects from each BEC can be made to cancel each other out, leaving behind the quantum fluctuations as the dominant effect within the system. This causes the system to change from a BEC gas to a liquid-like droplet. But this is far from your conventional liquid droplet: whereas, say, water is hard to compress because the electronic shells of neighbouring atoms refuse to overlap, in the quantum liquid it is because of quantum fluctuations. As such, the quantum droplet owes its existence to intrinsically quantum effects; this makes it a fascinating object to study. Moreover, it provides a platform to study quantum fluctuations, from their microscopic origins to their macroscopic manifestations.We will engineer quantum droplets, for the first time in the UK, using a mixture of caesium and ytterbium BECs; this atomic combination will enable us to exert high levels of control over the liquid. Given that this state has only recently been discovered, there is much to study and learn. We will use our experimental capabilities to push the droplets to their limits. We will map out the regimes for which they are supported, as well as the details of how they form. We will experimentally interrogate them in a range of scenarios, effectively prodding and pushing them, to understand how they respond. We will pay particular attention to effectively 2D and 1D geometries where quantum fluctuations are predicted to be greatly enhanced. Alongside our experiments, we will develop and test theoretical models to describe our observations; this will allow us to address open questions regarding the underlying physics and quantify the precise role of the quantum fluctuations. The findings of our work will be of fundamental importance in deepening our understanding of quantum fluctuations and may motivate applications of quantum droplets such as in precision spectroscopy and deposition.

如果我们在微观层面上深入观察自然，我们会发现一个由量子力学控制的奇怪世界，在那里我们的直觉崩溃了。在这个迷人的状态中，粒子的位置具有固有的不确定性，并且永远在波动。这种量子涨落是许多物理现象的核心，从范德华力到黑洞中的霍金辐射，并可能为基于量子效应的技术提供最终限制。然而，量子涨落很难用实验观察和理论上描述。自1995年实现以来，玻色-爱因斯坦凝聚体（BECs）为观察量子世界提供了一个独特的窗口。BEC是一种由相同原子组成的气体，冷却到比绝对零度高不到百万分之一度。在这一点上，单个原子位置的不确定性大于原子之间的距离，不可能识别单个原子。相反，这种气体的行为就像一股受量子力学支配的巨大物质波，并表现出一系列惊人的量子特性，比如能够干扰另一种BEC，能够无粘性流动（超流动性）。此外，BECs可以接受高度的实验控制（例如，在时间和空间上操纵和询问系统），并且可以以高分辨率成像。通过考虑所有原子的平均行为，即所谓的“平均场”，BECs的行为，包括上述性质，都得到了高度精确的捕获。自1995年以来，实验和理论工作的协同作用已经建立了对量子平均场及其如何影响系统行为的深刻理解。然而，在BEC中，量子涨落与平均场相比较小，因此，BEC所提供的优点尚未扩展到量子涨落领域。进入量子液滴。当两个BEC共存时，可以使每个BEC的平均场量子效应相互抵消，留下量子涨落作为系统内的主导效应。这使得系统从BEC气体变为液体状液滴。但这与传统的液滴相差甚远：如果说，水很难压缩是因为邻近原子的电子壳层拒绝重叠，那么在量子液体中，这是因为量子涨落。因此，量子液滴的存在本质上归功于量子效应；这使它成为一个迷人的研究对象。此外，它提供了一个研究量子涨落的平台，从它们的微观起源到它们的宏观表现。我们将在英国首次使用铯和镱BECs的混合物来设计量子液滴；这种原子组合将使我们能够对液体施加高水平的控制。考虑到这种状态是最近才被发现的，有很多东西需要研究和学习。我们将利用我们的实验能力将液滴推向极限。我们将描绘出他们所支持的政权，以及他们如何形成的细节。我们将实验性地在一系列场景中询问他们，有效地刺激和推动他们，以了解他们的反应。我们将特别关注有效的二维和一维几何形状，其中量子涨落被预测将大大增强。除了我们的实验，我们将开发和测试理论模型来描述我们的观察；这将使我们能够解决关于基础物理学的开放性问题，并量化量子涨落的精确作用。我们的研究结果将对加深我们对量子涨落的理解具有重要意义，并可能激发量子液滴在精密光谱和沉积等方面的应用。