Yui Satoshi, Tang Yuan, Guo Wei, Kobayashi Hiromichi, Tsubota Makoto
Department of Physics, Osaka Metropolitan University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan.
Nambu Yoichiro Institute of Theoretical and Experimental Physics (NITEP), Osaka Metropolitan University, Osaka 558-8585, Japan.
Phys Rev Lett. 2022 Jul 8;129(2):025301. doi: 10.1103/PhysRevLett.129.025301.
In classical viscous fluids, turbulent eddies are known to be responsible for the rapid spreading of embedded particles. However, in inviscid quantum fluids where the turbulence is induced by a chaotic tangle of quantized vortices, dispersion of the particles can be achieved via a nonclassical mechanism, i.e., their binding to the evolving vortices. However, knowledge on how the vortices diffuse and spread in quantum-fluid turbulence is very limited, especially for the so-called ultraquantum turbulence (UQT) generated by a random tangle of vortices. Here we report a systematic numerical study of the apparent diffusion of vortices in UQT in superfluid helium-4 using the full Biot-Savart simulation. We reveal that the vortices in the superfluid exhibit a universal anomalous diffusion (superdiffusion) at small times, which transits to normal diffusion at large times. This behavior is found to be the result of a generic scaling property of the vortex velocity. Our simulation at finite temperatures also nicely reproduces recent experimental observations. The knowledge obtained from this study may form the base for understanding turbulent transport and universal vortex dynamics in various quantum fluids.
在经典粘性流体中，已知湍流涡旋是导致嵌入粒子快速扩散的原因。然而，在无粘性量子流体中，湍流是由量子化涡旋的混沌缠结引起的，粒子的扩散可以通过一种非经典机制实现，即它们与演化中的涡旋结合。然而，关于涡旋在量子流体湍流中如何扩散和传播的知识非常有限，特别是对于由涡旋随机缠结产生的所谓超量子湍流（UQT）。在此，我们使用完整的毕奥-萨伐尔模拟，对超流氦-4中UQT涡旋的表观扩散进行了系统的数值研究。我们发现，超流体中的涡旋在短时间内呈现出普遍的反常扩散（超扩散），并在长时间后转变为正常扩散。这种行为被发现是涡旋速度的一种通用标度性质的结果。我们在有限温度下的模拟也很好地再现了最近的实验观测结果。从这项研究中获得的知识可能为理解各种量子流体中的湍流输运和通用涡旋动力学奠定基础。
