Novel Experiments in Multiphase Superfluid 3He at Ultralow Temperatures

超流体、超导体和玻色凝聚的稀气体是非常有趣的，因为它们的组成原子形成相干的基态，在其中整个系统的行为是相关的，导致宏观量子现象。3 He原子形成具有自旋和轨道角动量的原子对。质量、自旋和轨道运动都表现出相干的量子行为，从而产生一系列奇异的性质。这种额外的复杂性使得超流3 He可以存在于两个非常不同的相干相A和B中，这取决于温度和磁场。我们能够将超流3 He冷却到几乎所有原子都配对的温度，因此我们拥有几乎纯的量子态。通过施加适当形状的磁场分布，我们可以稳定不同区域中的不同相，具有各种几何形状，包括被A相包围的B相的孤立气泡。气泡的几何形状将使我们能够研究基本过程，否则可能会受到壁的影响，如相成核，热输运和湍流。A-B界面是分离两个高度相干相的相干结构。序参量必须在从一个相位到另一个相位的交叉中进行复杂的旋转，使质量、自旋和轨道自由度平滑地匹配。这个独特的系统为我们提供了一个进入广泛的新物理学的入口。这显然是一个有趣的系统本身。然而，它也为较难访问的系统提供了一个模型。例如，它是我们实验室中最接近宇宙膜（时空中的等效结构）的东西。通过碰撞两个A-B边界，我们可以在实验室中模拟膜湮灭。通过将气凝胶浸入3 He中，我们可以研究气凝胶中纳米尺寸的二氧化硅链引起的无序所产生的脏极限中的超流相。此外，当我们将气凝胶浸入超流体中时，几个原子层的3 He原子被吸附到二氧化硅链上，从而在氦-气凝胶系统中形成实质性的固体3 He组分。固体3 He具有高磁性，并且与流体紧密接触。这为在固体上使用磁冷却技术和近乎完美的热接触来冷却超流体提供了独特的机会。硅线周围的固体层形成了一个3 He纳米管系统，它也有可能揭示新的令人兴奋的物理学。我们打算开发一个3 He气凝胶冷却台来研究固体3 He纳米管和冷却超流到一个新的低温区，在那里基本上没有热激发超过宏观体积的液体。最近，我们还发现，超流3 He提供了一个特别有用的工具，在低温下研究量子湍流。量子湍流本质上是量子涡线的缠结（线缺陷，超流循环在其周围被量子化）。量子湍流与经典湍流有着密切的相似之处，但由于量子化的涡旋和缺乏粘性，量子湍流要简单得多，因此可能会为理解湍流提供更好的见解。我们计划使用高灵敏度的量热技术，我们已经开发出，以测量量子湍流的能量衰减在零温度限制，提供更好的基本衰变mechanism. Finally信息，我们正在使用这些实验，以试点开发一种新形式的高灵敏度石英谐振器，定制设计，以最大限度地提高其与超流3 He在最低温度下的相互作用。我们希望这将取代目前普遍存在的振弦谐振器（也是在兰开斯特开发的）作为标准的低温量子流体传感器/温度计。

Superfluids, superconductors and Bose condensed dilute gases are extremely interesting since their constituent atoms form coherent ground states, in which the behaviour of the whole system is correlated, leading to macroscopic quantum phenomena.However, superfluid 3He is unique due to its multi-component order parameter. The 3He atoms form pairs which have both spin and orbital angular momentum. The mass, spin and orbital motions each exhibit coherent quantum behaviour giving rise to a whole range of exotic properties. This added complexity allows superfluid 3He to exist in two very different coherent phases, A and B, depending on the temperature and magnetic field.We are able to cool superfluid 3He to temperatures where virtually all atoms are paired, so we have an almost pure quantum state. By applying a suitably shaped magnetic field profile we can stabilise different phases in different regions, with various geometries including an isolated bubble of B-phase surrounded by A-phase. The bubble geometry will allow us to study fundamental processes, which might otherwise be influenced by walls, such as phase nucleation, thermal transport and turbulence.The A-B interface is a coherent structure separating two highly coherent phases. The order parameter must make a complex pirouette in crossing from one phase to the other, matching-up smoothly the mass, spin and orbital degrees of freedom. This unique system gives us an entre into a wide range of new physics. It is clearly an interesting system in its own right. However, it also provides a model for less accessible systems. For example, it is the nearest thing we have in the laboratory to a cosmological brane (equivalent structures in space-time). By colliding two A-B boundaries, we can simulate brane-annihilations in the laboratory. These are of fundamental interest to the braneworld scenarios of cosmology.By immersing aerogel in 3He we can study the superfluid phases in the dirty limit generated by the disorder induced by the nanometre sized silica strands in the aerogel. Furthermore, when we immerse the aerogel in superfluid, a few atomic layers of 3He atoms are adsorbed onto the silica strands to make a substantial solid 3He component in the helium-aerogel system. The solid 3He is highly magnetic and is in intimate contact with the fluid. This provides a unique opportunity for using magnetic cooling techniques on the solid and the near perfect thermal contact to cool the superfluid. The solid layers around the silica strands form a system of 3He-nanotubes which also have potential for revealing new exciting physics. We intend to develop a 3He-aerogel cooling stage to study both the solid 3He-nanotubes and to cool the superfluid to new a low temperature regime where there are essentially no thermal excitations over macroscopic volumes of the liquid.Recently, we have also found that superfluid 3He provides a particularly useful tool for studying quantum turbulence at low temperatures. Quantum turbulence is essentially a tangle of quantum vortex lines (line defects around which the superfluid circulation is quantised). Quantum turbulence has close analogues with classical turbulence but is much simpler, due to the quantised vortices and lack of viscosity, and might therefore provide better insights to understanding turbulence in general. We plan to use highly sensitive calorimetric techniques, which we have developed earlier, to measure the energy decay of quantum turbulence in the zero temperature limit, providing better information on fundamental decay mechanisms.Finally we are using these experiments to pilot the development of a new form of the highly sensitive quartz resonator, custom-designed to maximise its interaction with superfluid 3He at the lowest temperatures. We hope that this will replace the currently ubiquitous vibrating wire resonator (also developed at Lancaster) as the standard low temperature quantum fluids sensor/thermometer.