Investigation of universal non-equilibrium dynamics using coupled 2-D quantum systems

使用耦合二维量子系统研究普遍非平衡动力学

• 批准号: EP/X024601/1
• 负责人: Christopher Foot
• 金额: $ 80.56万
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FX024601%2F1
• 关键词: Investigation; universal; non; equilibrium; dynamics

Systems that are not in equilibrium are ubiquitous but can be complex to describe. Systems at equilibrium are described with great success by statistical mechanics but there are no general theoretical framework for how closed many-body quantum systems evolve to reach such thermalised states. Examples range from the cooling of a cup of coffee to the emergence of structures in the early universe. Non-equilibrium (NEQ) processes are also important for quantum systems including quantum computers such as those based on superconducting qubits. Our experimental techniques allow many-body quantum systems to be prepared in precisely defined NEQ situations and then track their evolution towards equilibrium in unprecedented level of detail.The system that we will use to gain a better understanding of NEQ physics is a two-dimensional (2D) gas of atoms at temperatures of tens of nanokelvin. The properties of 2D systems are of central importance in physics and part of the Nobel prize for Physics (2016) was awarded to Kosterlitz and Thouless for their work on a phase transition in 2D systems that is named after them, the Berezinskii-Kosterlitz-Thouless (BKT) transition. This transition occurs as the 2D quantum gas is cooled and, at a certain temperature, it changes into a superfluid that flows without friction amongst other fascinating properties.The ultracold atoms are trapped in extremely well-controlled conditions thus enabling us to make definitive quantitative comparisons with theoretical expectations. Quantum systems confined to 2D are especially interesting for studying NEQ processes because the fluctuations, that are an inherent part of quantum mechanics, play a large role in preventing true long-range order. This approach will provide insights into similar phase transitions in other 2D systems such as thin-film superconductors and liquid crystals, and the quantum gas acts as a quantum simulator of 2D quantum physics in general.A key factor that enables the proposed investigation is the double-well potential for ultracold rubidium atoms that we have created by an innovative use of combined radiofrequency (RF) and static magnetic fields. With this technique we have realised a bilayer of 2D quantum gases where the inter-layer distance is controlled with a precision of tens of nanometres, which is impossible with alternative (optical) methods that are widely used. This allows the quantum coupling between two layers to be set to precise values, and we use the programmability of modern RF electronics to implement dynamical control of the double-well potential with nanosecond resolution. A further advantage of having two layers, is that we can use matter-wave interference of the ultracold atoms to probe the microscopic phase fluctuations of the system that are intrinsic in 2D quantum gases.This allows us to probe the local vortex density and first-order correlation functions which are the key to understanding BKT physics. Further technical improvement will allow the detection of higher-order correlations, as well as the full probability distribution function of the fluctuating observables, which represent the essence of quantum observables. Using this cold-atom apparatus as a 'quantum simulator' of many-body phases in 2D systems will provide fresh insights. These experimental techniques have been developed and refined to the level at which the quantum tunnelling between the two wells is controllable and this state-of-the-art apparatus enables the experimental investigation of long-standing research questions.

不处于平衡的系统无处不在，但可以描述复杂。统计力学取得了巨大的成功描述了平衡的系统，但是对于封闭的多体量子系统如何发展以达到此类热态状态，没有一般的理论框架。例子范围从冷却一杯咖啡到早期宇宙中结构的出现。非平衡（NEQ）过程对于包括量子计算机（例如基于超导量子）的量子系统也很重要。我们的实验技术允许在精确定义的NEQ情况下制备多体量子系统，然后在前所未有的细节级别跟踪其朝着平衡的进化。我们将使用该系统来更好地了解NEQ物理学的系统是二维（2D）原子的二维（2D）原子的气温，在Nanokelvin的nanokelvin的温度下。 2D系统的特性在物理学中至关重要，诺贝尔物理奖（2016）的一部分被授予Kosterlitz和Thouless，因为他们在2D系统中的阶段过渡方面的工作，该系统以它们命名，Berezinskii-Kosterlitz-bkt-therless-thy-thy-thouble（bkt）过渡。由于2D量子气的冷却，并且在一定温度下，它变成了一个超流体，该超流体在其他引人入胜的特性中不摩擦而变化。超低原子被捕获在非常控制的条件下，使我们能够使我们与理论期望进行明确的定量比较。限制在2D的量子系统对于研究NEQ过程特别有趣，因为这是量子力学的固有部分的波动，在防止真实的远距离顺序中起着重要作用。 This approach will provide insights into similar phase transitions in other 2D systems such as thin-film superconductors and liquid crystals, and the quantum gas acts as a quantum simulator of 2D quantum physics in general.A key factor that enables the proposed investigation is the double-well potential for ultracold rubidium atoms that we have created by an innovative use of combined radiofrequency (RF) and static magnetic fields.通过这种技术，我们已经意识到了一个双层二量子气体的双层，其中层间距离的精度是数十纳米的精确度，这是不可能使用广泛使用的替代（光学）方法来控制的。这允许将两层之间的量子耦合设置为精确值，并且我们使用现代RF电子设备的可编程性来实现对纳米秒分辨率的双孔电势的动态控制。拥有两层的另一个优点是，我们可以使用超电原子的物质波干扰来探测系统内固有的微观相位波动，这些相位是2D量子气体中固有的。这使我们能够探测局部涡流密度和一阶相关功能，这是理解BKT物理学的关键。进一步的技术改进将允许检测高阶的相关性，以及波动可观察物的完整概率分布函数，这代表了量子可观察到的本质。在2D系统中，将这种冷原子设备作为多体相的“量子模拟器”将提供新的见解。这些实验技术已经开发并完善，达到了两个井之间的量子隧穿的水平，并且这种最新的设备可以对长期研究问题进行实验研究。