Superfluid 3He Far from Equilibrium

该奖学金计划响应了EPSRC的号召，以解决远离平衡的系统物理学和紧急现象物理学领域的突出重大挑战。我的愿景是通过研究具有既定理论框架的知名系统-超流3 He中的非平衡现象来应对这些挑战。相干凝聚体（或超流体）是我们拥有的最简单的“复杂”系统，因为凝聚体仅由一个描述整个宏观系综的全局波函数控制。这种简单性使它们成为研究和测试涵盖从亚核到宇宙学的大量显然无关的物理系统的想法的理想场所。这里有趣的是，超流体绝对是研究远离平衡的系统的理想选择，也有大量的涌现现象。相干凝聚体（或者至少是我们在实验上可以获得的凝聚体）是只存在于非常低的温度下的脆弱物体。这几乎是独一无二的，这意味着我们可以在整个条件范围内研究它们，从几乎零熵，零温度的静止状态，一直到我们完全破坏相干性的状态。产生和研究远离平衡态的最简单形式对于创建可证伪的理论和可靠的数值模型至关重要。通过理解最简单的状态，我们可以进一步理解更复杂的现象，调整理论模型，因为它们确实适用于更简单的情况。也就是说，在这个应用程序中，我提出了几个实验，把我们的模型冷凝物，超流3 He，到极限。这里的主要兴趣是，尽管感知智慧表明，一致性的破坏是很好理解的，但在现实中，这与真理相去甚远。这是“常识”，当我们移动一个散射体通过超流，然后在某个临界速度的超流应该灾难性地打破，并返回系统的正常状态。最近，我们在兰开斯特表明，这不会发生在超流3 He的速度远远超过公认的朗道值。这倒是让人有些意外。在拟议的实验方案中，我的目标是找到超临界超电流的存在的原因，它围绕着散射体流动，并找到它们的稳定域。为此，我将利用核磁共振的组合探测凝聚物的波函数，并使用一种能够在凝聚物中匀速运动的装置--这是最近在超流体研究技术中开创的一项新技术。首次使用核磁共振与超低温下3 He中稳定超流的强大组合，也将使我们能够研究几种涌现现象。例如，超流3 He系统是研究不同超流相之间的量子临界相变的理想介质，可以通过改变温度绝对零度附近的超流压力来获得。

This fellowship proposal answers the EPSRC's call to tackle outstanding grand challenges in the areas of physics of systems far from equilibrium and physics of emergent phenomena. My vision is to approach these challenges by studying non-equilibrium phenomena in a well-known system with an established theoretical framework - superfluid 3He. Coherent condensates (or superfluids) are the simplest "complex" systems that we have, in that the condensate is governed by just one global wave function describing the whole macroscopic ensemble. This simplicity makes them ideal playgrounds for studying and testing ideas that cover a vast range of apparently unrelated physical systems from the subnuclear to the cosmological. Of interest here, superfluids are absolutely ideal for studying systems far from equilibrium and also host an abundance of emergent phenomena. Coherent condensates (or at least those to which we have experimental access) are fragile objects only existing at very low temperatures. Almost uniquely that means that we can study them over the whole range of conditions from the virtually zero-entropy zero-temperature quiescent state all the way through to the regime where we have the complete destruction of the coherence. Producing and studying the simplest forms of states far from equilibrium is essential for creating falsifiable theories and reliable numerical models. By understanding the simplest states we can progress to the understanding of more complex phenomena, adjusting the theoretical models with the firm knowledge that they do work in simpler situations. That said, in this application I propose several experiments which take our model condensate, superfluid 3He, to the limit. The main interest here is that although perceived wisdom suggests that the destruction of coherence is pretty well understood, in reality that is very far from the truth. It is "common knowledge" that when we move a scatterer through a superfluid, then at some critical velocity the superfluidity should catastrophically break down and return the system to the normal state. Recently, we have shown at Lancaster that this does not happen in superfluid 3He up to velocities well in excess of the accepted Landau value. This was quite unexpected. In the proposed experimental programme I will aim to find the reason for the existence of supercritical supercurrents which flow around the scatterer and also find the domain of their stability. To this end I will utilise a combination of nuclear magnetic resonance to probe the condensate's wave function with a device capable of uniform motion through the condensate - a recently pioneered addition to the arsenal of the superfluid research techniques.Using for the first time the powerful combination of nuclear magnetic resonance with steady superflow in 3He at ultralow temperatures will also enable us to investigate several emergent phenomena. For example, the superfluid 3He system is an ideal medium for the study of quantum critical phase transitions between different superfluid phases which can be accessed by changing the pressure of the superfluid near the absolute zero of temperature.