Pushing the boundaries of superfluid vacuum and coherence

超流体、超导体和原子气体凝聚等宏观量子系统将量子物理带入了肉眼可以观察到的范围。这些量子相干现象起源于实验室，但现在要么已经用于商业应用(例如超导体)，要么正在考虑技术应用而积极开发(例如玻色凝聚体)。与此同时，我们关于这些系统的知识不断扩展，揭示了前所未有的现象：最近发现的时间晶体就是一个很好的例子，它打破了永动机绝对不可能的事实。拟议的研究计划将探索超流3He中宏观量子秩序的边缘。超流3He是一个具有极其丰富现象学的宏观量子系统，触及高能物理、宇宙学等看似遥远的领域。最著名的例子是希格斯机制，它最初是在超导体(-流体)系统中发现的，后来成为粒子物理标准模型的一部分。另一个例子是Kibble-Zurek机制，最初是一种宇宙学推测，它是在超流3He中发现的，现在构成了现代实验室物理学的基石。从力学角度理解低温超流3He的正确方法是考虑真空，在真空中，棒可以四处移动，就好像超流体一开始就不在那里一样。只有当探测超过真空的固有阈值时，例如由库珀对大小设置的最小尺寸或由超流能量隙设置的最大速度，真空的量子本质才会被揭示。这意味着真空不再是背景，开始与探测器相互作用。例如，一个足够小的探测器将揭示真空的内在结构，而这个结构对大型探测器是隐藏的。本征结构的一个意想不到的推论是，超流体的表面形成了一个几乎与三维主体分离的二维系统：将一根棒移动到表面附近，释放的任何能量都将粘在表面上。超流体的磁性在很大程度上取决于从块状真空中涌出的磁性粒子的动力学。这些粒子可以形成时间晶体，这是物质在永久重复运动中的动态相态。其他“时间阶段”，如无序的时间液体，可以用类似的方法来创造，并通过利用平衡物理学的工具箱来探索动态系统来解释。这项研究将从力学和磁学的角度探索量子真空：1.我将通过在几百纳米厚的超流3He表面层中进行一系列输运实验来领导对表面束缚费米子的探索。在实践中，这意味着在一个点加热表层，并通过测量表面另一点的温度来观察热量是如何沿着表面流动的。为该项目委托的技术还将允许通过在超流体的主体中移动一个微小的杆来揭示超流体真空的内在结构，在那里，与真空的相互作用在小于库珀对半径的尺度上发生显著变化。1.我的团队将通过熔化量子时间晶体来创造一种新的玻色子物质相，这种物质会自发地变得不相干--时间液体。熔化过程是通过增加颗粒密度来启动的。绘制超流真空中“时间相”的相图将巩固这一新的研究领域。该项目得到了东道主机构和国际上领先的技术、实验和理论合作者的支持。这一奖学金带来的发现将引领具有学术和技术影响的新研究领域，从束缚费米子的二维物理到基于磁振子的室温量子设备。

Macroscopic quantum systems such as superfluids, superconductors, and atomic gas condensates bring quantum physics to scales observable by the naked eye. These quantum-coherent phenomena originated in the laboratory but are now either already used for commercial applications (for example superconductors) or being actively developed with technological applications in mind (for example Bose condensates). At the same time the edges of our knowledge about these systems keep being extended, revealing unprecedented phenomena: a good example is the recent discovery of time crystals that bend the categorical impossibility of perpetual motion machines. The proposed research programme will explore the edges of macroscopic quantum order in superfluid 3He. Superfluid 3He is a macroscopic quantum system with extremely rich phenomenology, touching seemingly distant fields such as high-energy physics and cosmology. The most famous example is the Higgs mechanism, which was originally discovered in a superconductor (-fluid) system and later become a part of the Standard Model of particle physics. Another example is the Kibble-Zurek mechanism, originally a cosmological speculation, which was discovered in superfluid 3He and now forms a cornerstone of modern laboratory physics. The right way to understand low-temperature superfluid 3He from a mechanical perspective is to think about a vacuum where a rod can be moved around as if the superfluid is not there in the first place. Only if the probing exceeds an intrinsic threshold of the vacuum, such as a minimum size set by the Cooper pair size or a maximum velocity set by the superfluid energy gap, will the quantum nature of the vacuum be revealed. This means that the vacuum ceases to be a background and starts interacting with the probe. For example, a probe that is small enough will reveal the intrinsic structure of the vacuum which is hidden from large probes. An unexpected corollary of the intrinsic structure is that the surfaces of the superfluid form a two-dimensional system nearly detached from the three-dimensional bulk: move a rod near the surface and any energy released will be stuck to the surface. The magnetic properties of the superfluid are largely determined by the dynamics of magnetic particles emerging from the bulk vacuum. These particles can form a time crystal, a dynamic phase of matter in permanent repeating motion. Other "time phases" such as disordered time liquids can be created with a similar approach and explained by harnessing the toolbox of equilibrium physics to explore dynamic systems. This fellowship will explore the quantum vacuum mechanically and magnetically: 1. I will lead the exploration of the surface-bound fermions by carrying out a series of transport experiments in the few hundred nanometre thick surface layer of superfluid 3He. In practice this means heating the surface layer at one point and observing how the heat flows along the surface by measuring temperature at another point on the surface. The technology commissioned for this project will also allow revealing the superfluid vacuum's intrinsic structure by moving a tiny rod in the bulk of the superfluid where the interaction with the vacuum dramatically changes at scales smaller than Cooper pair radius. 1. My team will create a new bosonic phase of matter which spontaneously becomes incoherent - a time liquid - by melting a quantum time crystal. The melting process is initiated by increasing the particle density. Mapping the phase diagram of the "time phases" in the superfluid vacuum will cement this new field of study. This project is backed by leading technical, experimental and theoretical collaborators in the Host Institution and internationally. Discoveries delivered by this fellowship will lead new fields of research with academic and technological implications spanning from two-dimensional physics of bound fermions to magnon-based room temperature quantum devices.