Tang Yuan, Bao Shiran, Guo Wei
The Cryogenics Laboratory, National High Magnetic Field Laboratory, Tallahassee, FL 32310.
Mechanical Engineering Department, Florida State University, Tallahassee, FL 32310.
Proc Natl Acad Sci U S A. 2021 Feb 9;118(6). doi: 10.1073/pnas.2021957118.
Generic scaling laws, such as Kolmogorov's 5/3 law, are milestone achievements of turbulence research in classical fluids. For quantum fluids such as atomic Bose-Einstein condensates, superfluid helium, and superfluid neutron stars, turbulence can also exist in the presence of a chaotic tangle of evolving quantized vortex lines. However, due to the lack of suitable experimental tools to directly probe the vortex-tangle motion, so far little is known about possible scaling laws that characterize the velocity correlations and trajectory statistics of the vortices in quantum-fluid turbulence, i.e., quantum turbulence (QT). Acquiring such knowledge could greatly benefit the development of advanced statistical models of QT. Here we report an experiment where a tangle of vortices in superfluid He are decorated with solidified deuterium tracer particles. Under experimental conditions where these tracers follow the motion of the vortices, we observed an apparent superdiffusion of the vortices. Our analysis shows that this superdiffusion is not due to Lévy flights, i.e., long-distance hops that are known to be responsible for superdiffusion of random walkers. Instead, a previously unknown power-law scaling of the vortex-velocity temporal correlation is uncovered as the cause. This finding may motivate future research on hidden scaling laws in QT.
通用标度律，如柯尔莫哥洛夫5/3律，是经典流体湍流研究的里程碑式成就。对于诸如原子玻色 - 爱因斯坦凝聚体、超流氦和超流中子星等量子流体，在存在不断演化的量子化涡旋线的混沌缠结时，湍流也可能存在。然而，由于缺乏合适的实验工具来直接探测涡旋缠结的运动，到目前为止，对于表征量子流体湍流（即量子湍流，QT）中涡旋的速度相关性和轨迹统计的可能标度律知之甚少。获得此类知识将极大地有益于QT先进统计模型的发展。在此，我们报告一项实验，其中超流氦中的涡旋缠结用固化的氘示踪粒子进行了标记。在这些示踪粒子跟随涡旋运动的实验条件下，我们观察到涡旋明显的超扩散。我们的分析表明，这种超扩散并非源于列维飞行，即已知导致随机游走者超扩散的长距离跳跃。相反，发现涡旋速度时间相关性的一种先前未知的幂律标度是其原因。这一发现可能会推动未来对QT中隐藏标度律的研究。
