Quasiparticle Imaging and Superfluid Flow Experiments at Ultralow Temperatures

超低温下的准粒子成像和超流体流动实验

• 批准号: EP/I028285/1
• 负责人: Viktor Tsepelin
• 金额: $ 119.16万
• 依托单位: Lancaster University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2011
• 资助国家: 英国
• 起止时间: 2011 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FI028285%2F1
• 关键词: Quasiparticle; Imaging; Superfluid; Flow; Experiments

Our group has pioneered novel techniques to cool superfluid 3He to ultra-low temperatures where thermal quasiparticle excitations are highly ballistic, having intrinsic mean-free-paths which approach kilometre length scales. Superfluid 3He displays a wide range of exotic spin, orbital and mass superfluid behaviour, providing an ideal system to study and to gain a better understanding of quantum systems in general. We have developed techniques to generate beams of ballistic quasiparticles and scatter them from various obstacles formed in the superfluid. Superfluid structures such as vortices, textures and phase boundaries have a large cross-section for Andreev reflection (a form of near-perfect retro-reflection of excitations unique to superfluids and superconductors), so are readily probed by excitation beams. We aim to further develop the techniques to build a quasiparticle camera to directly image superfluid structures providing time and spatial resolution to study their dynamics.We will first apply the technique to image the beam of excitations which is emitted by a vibrating wire above some critical velocity. The excitations are created by the wire as it breaks apart the `paired-atom' superfluid condensate. Quantum vortices (line defects in the superfluid with a well-defined circulating flow) are also produced above this critical velocity. The two processes appear to be closely linked, but the mechanism is not understood. The images will allow us to simultaneously observe the pair-breaking beam and vortices, which will provide detailed information about the generation processes.At higher velocity amplitudes, vibrating wires produce quantum turbulence, a complex tangle of vortex lines. Despite its overwhelming importance to a wide range of science and technology, turbulence in general is poorly understood. Quantum turbulence is conceptually much simpler than classical turbulence and is far more amenable to computer simulation. The study of superfluid turbulence may thus eventually provide a better understanding of turbulence in general. There are several interesting unanswered questions to be addressed in quantum turbulence, such as how it develops and decays in the absence of viscous forces at low temperatures. We aim to use the new imaging techniques to directly image quantum turbulence to provide detailed dynamical information for direct comparison with theory.We will also develop a new technique to allow very precise controlled motion of an object in the superfluid to study various flow related properties. In particular, it will allow a comprehensive study of the pair-breaking mechanism over a wide frequency range, including near-uniform (zero frequency) flow. This is interesting since the mechanism is thought to involve the population of bound surface states (including so-called Majorana states which have received a great deal of recent theoretical interest) and there may be analogies with quantum Hawking radiation.The flow device will also allow us to measure extremely low velocities. This will enable us to explore possible supersolid behaviour in solid 4He at low temperatures by measuring the slow motion of a wire through the solid. Supersolidity is a very exotic phenomenon, predicted by some theories, where a quantum solid can exhibit frictionless flow. There is widespread speculation that supersolidity has been observed in 4He at low temperatures, but the observations might also be explained by defects in the solid with superfluid cores. This topic remains highly controversial and has received a great deal of interest. The current device will be very sensitive to both defects and supersolid flow, thus providing key information to resolve this issue.We will also investigate new avenues for research in exotic superfluid phases, spin superfluidity and high frequency/small length scale phenomena. The new techniques developed will be very versatile with a wide range of future applications.

我们的团队开创了将超流体3He冷却到超低温的新技术，在超低温下，热准粒子激发具有高度弹道性，具有接近公里长度尺度的固有平均自由路径。他展示了广泛的奇异自旋、轨道和质量超流体行为，为研究和更好地理解量子系统提供了一个理想的系统。我们已经开发出技术，可以产生弹道准粒子束，并将它们从超流体中形成的各种障碍物中散射出去。超流体结构，如漩涡、结构和相边界，对于Andreev反射（一种超流体和超导体特有的近乎完美的反向反射形式）具有很大的横截面，因此很容易被激发光束探测到。我们的目标是进一步发展建立准粒子相机的技术，以直接成像超流体结构，提供时间和空间分辨率来研究它们的动力学。我们将首先应用该技术对超过某一临界速度的振动导线发出的激励束进行成像。这些激发是由导线在分解“对原子”超流体冷凝物时产生的。量子涡旋（具有明确循环流动的超流体中的线缺陷）也在此临界速度以上产生。这两个过程似乎密切相关，但其机制尚不清楚。这些图像将使我们能够同时观察到对断裂的光束和漩涡，这将提供有关产生过程的详细信息。在更高的速度振幅下，振动的电线会产生量子湍流，这是一种复杂的漩涡线。尽管湍流对科学技术的广泛应用具有压倒性的重要性，但人们对它的总体理解却很少。量子湍流在概念上比经典湍流简单得多，而且更易于计算机模拟。因此，对超流体湍流的研究可能最终提供对一般湍流更好的理解。在量子湍流中有几个有趣的未解决的问题需要解决，比如在低温下没有粘性力的情况下它是如何发展和衰变的。我们的目标是利用新的成像技术直接成像量子湍流，以提供详细的动力学信息，以便与理论直接比较。我们还将开发一种新技术，允许超流体中物体的非常精确的控制运动，以研究各种与流动相关的特性。特别是，它将允许在广泛的频率范围内，包括近均匀（零频率）流对断裂机制的全面研究。这是很有趣的，因为这种机制被认为涉及到束缚表面态的总体（包括所谓的马约拉纳态，它最近受到了大量的理论关注），并且可能与量子霍金辐射有相似之处。流动装置也将允许我们测量极低的速度。这将使我们能够通过测量导线在固体中的缓慢运动来探索低温下固体4He中可能的超固体行为。超固体是一种非常奇特的现象，一些理论预测，量子固体可以表现出无摩擦流动。人们普遍推测氦氦在低温下可以观察到超固体，但这些观察结果也可以用具有超流体核的固体中的缺陷来解释。这个话题仍然很有争议，并引起了很大的兴趣。目前的设备将对缺陷和超固体流动都非常敏感，从而为解决这一问题提供关键信息。我们还将探索奇异超流体相、自旋超流体和高频/小长度尺度现象的研究新途径。所开发的新技术将是非常通用的，具有广泛的应用前景。

项目成果

Thermometry in Normal Liquid 3He Using a Quartz Tuning Fork Viscometer

使用石英音叉粘度计测量正常液体 3He 的温度

• DOI: 10.1007/s10909-012-0804-3
• 发表时间: 2012
• 期刊: Journal of Low Temperature Physics
• 影响因子: 2
• 作者: Bradley D

A New Device for Studying Low or Zero Frequency Mechanical Motion at Very Low Temperatures

• DOI: 10.1007/s10909-011-0388-3
• 发表时间: 2011-11-01
• 期刊: JOURNAL OF LOW TEMPERATURE PHYSICS
• 影响因子: 2
• 作者: Bradley, D. I.;Clovecko, M.;Williams, P.
• 通讯作者: Williams, P.

Fundamental dissipation due to bound fermions in the zero-temperature limit.

• DOI: 10.1038/s41467-020-18499-1
• 发表时间: 2020-09-21
• 期刊: Nature communications
• 影响因子: 16.6
• 作者: Autti S;Ahlstrom SL;Haley RP;Jennings A;Pickett GR;Poole M;Schanen R;Soldatov AA;Tsepelin V;Vonka J;Wilcox T;Woods AJ;Zmeev DE
• 通讯作者: Zmeev DE

Visualizing Pure Quantum Turbulence in Superfluid 3He: Andreev Reflection and its Spectral Properties.

• DOI: 10.1103/physrevlett.115.015302
• 发表时间: 2015-03
• 期刊: Physical review letters
• 影响因子: 8.6
• 作者: A. Baggaley;V. Tsepelin;C. Barenghi;S. Fisher;G. Pickett;Y. Sergeev;N. Suramlishvili

Response of a Mechanical Oscillator in Solid 4He

固体 4He 中机械振荡器的响应

• DOI: 10.1007/s10909-013-0930-6
• 发表时间: 2013
• 期刊: Journal of Low Temperature Physics
• 影响因子: 2
• 作者: Ahlstrom S