超流氦纳米液滴并合中的涡量和量子turbulence
Vorticity and quantum turbulence in the merging of superfluid Helium nanodroplets
摘要：
本文研究了两个$^4$ He液滴在零温下由于范德华相互吸引而引起的并合。在合并的早期阶段，密度结构出现，这与Vicente等人的实验观察结果非常吻合[J. Low Temp. 121，627（2000）]。当液滴合并时，量子化的涡旋-反涡旋环对在表面成核，并在合并的液滴内部湮灭，产生旋转子爆发。我们还观察到量子化的涡旋-反涡旋环的成核，这些环包裹着液滴表面并保持在表面上，直到它们最终衰减成短波长的表面波。动能谱的分析揭示了存在一种状态，其中由涡旋相互作用和湮灭引起的湍流的特征在于Kolmogorov幂律。其次是另一个制度，其中旋子辐射（产生的涡旋-反涡旋湮灭）占主导地位，其标志是一个弱，湍流表面动力学。我们认为，类似的过程可能会出现在超流氦液滴后，他们捕获杂质，或者如果他们产生的流体动力学不稳定的液体射流。最近发现的自束缚玻色-爱因斯坦凝聚体之间的碰撞实验应该显示出类似的现象。
英文摘要：
We have studied the merging of two $^4$He droplets at zero temperature, caused by their Van der Waals mutual attraction. During the early stages of the merging, density structures appear which closely match the experimental observations by Vicente et al. [J. Low Temp. Phys. 121, 627 (2000)]. When the droplets are merging, quantized vortex-antivortex ring pairs nucleate at the surface and annihilate inside the merged droplet producing a roton burst. We also observe the nucleation of quantized vortex-antivortex rings that wrap the droplet surface and remain localized on the surface until they eventually decay into short-wavelength surface waves. Analysis of the kinetic energy spectrum discloses the existence of a regime where turbulence caused by vortex interaction and annihilation is characterized by a Kolmogorov power law. This is followed by another regime where roton radiation (produced by vortex-antivortex annihilation) dominates, whose hallmark is a weak, turbulent surface dynamics. We suggest that similar processes might appear in superfluid helium droplets after they capture impurities or if they are produced by hydrodynamic instability of a liquid jet. Experiments on collisions between recently-discovered self-bound Bose-Einstein condensates should display a similar phenomenology.
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