We observe an inverse turbulent-wave cascade, from small to large length scales, in a driven homogeneous 2D Bose gas. Starting with an equilibrium condensate, we drive the gas isotropically on a length scale much smaller than its size, and observe a nonthermal population of modes with wavelengths larger than the drive one. At long drive times, the gas exhibits a steady nonthermal momentum distribution. At length scales increasing from the drive one to the system size, this distribution features in turn: (i) a power-law spectrum with an exponent close to the analytical result for a particle cascade in weak-wave turbulence, and (ii) a spectrum reminiscent of a nonthermal fixed point associated with universal coarsening in an isolated 2D gas. In further experiments, based on anisotropic driving, we reveal the complete qualitative picture of how the steady-state cascade forms. Published by the American Physical Society 2024

中文翻译：

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在驱动量子气体中观察逆湍流波级联


我们在驱动的均匀 2D 玻色气体中观察到从小到大长度尺度的逆湍流波级联。从平衡凝结物开始，我们在远小于其尺寸的长度尺度上各向同性地驱动气体，并观察到波长大于驱动波长的非热模式群。在较长的驾驶时间里，气体表现出稳定的非热动量分布。当长度尺度从驱动器 1 增加到系统大小时，这种分布反过来具有：（i） 指数接近弱波湍流中粒子级联的解析结果的幂律谱，以及 （ii） 让人想起与孤立二维气体中的普遍粗化相关的非热固定点的谱。在进一步的实验中，基于各向异性驱动，我们揭示了稳态级联如何形成的完整定性图景。 美国物理学会 2024 年出版