Observation of universal dynamics in a spinor Bose gas far from equilibrium
Observation of universal dynamics in a spinor Bose gas far from equilibrium
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DOI：
10.1038/s41586-018-0659-0
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发表时间：
2018-05
期刊：
影响因子：
64.8
通讯作者：
Maximilian Prüfer;Philipp Kunkel;H. Strobel;S. Lannig;D. Linnemann;Christian-Marcel Schmied;J. Berges;T. Gasenzer;M. Oberthaler
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文献类型：
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作者：
Maximilian Prüfer;Philipp Kunkel;H. Strobel;S. Lannig;D. Linnemann;Christian-Marcel Schmied;J. Berges;T. Gasenzer;M. Oberthaler
预测远离平衡的量子系统的动力学是理论多体物理中最具挑战性的问题之一。虽然多体系统的演化在所有细节上通常都是棘手的，但相关的可观测数据可能会变得对微观系统参数和初始条件不敏感。这是普遍性现象的基础。普适性是通过系统时空演化的尺度来确定的，而不是通过平衡，而是通过普适指数和函数来捕捉的。从理论上讲，这已经在不同的例子中得到了研究，如膨胀宇宙宇宙学中的再热过程，用量子色动力学描述的核碰撞实验的动力学，以及非相对论量子场论中稀薄量子气体的后失超动力学，…，-。然而，量子多体系统在空间和时间上的这种标度演化的实验演示一直缺乏。在这里，我们通过评估准一维自旋玻色-爱因斯坦凝聚体中的空间分辨自旋关联来观察宇宙动力学的出现。对于较长的演化时间，我们从自旋激发的空间关联中提取标度性质。由此我们发现，动力学由浮现的守恒量和自旋激发向低动量尺度的输运所支配。我们的结果建立了一类重要的非平稳系统，其动力学用与时间无关的标度指数和函数编码，表明非热不动点的存在。我们证实，通过准备不同的初始条件并观察相同的标度行为，非热标度现象不涉及参数的微调。我们的类比量子模拟方法为揭示非热普适类的基本机制和特征提供了基础。人们可以利用这种普适性从超冷气体的实验中学习宇宙学和量子色动力学中研究的动力学的基本方面。
Predicting the dynamics of quantum systems far from equilibrium represents one of the most challenging problems in theoretical many-body physics,. While the evolution of a many-body system is in general intractable in all its details, relevant observables can become insensitive to microscopic system parameters and initial conditions. This is the basis of the phenomenon of universality. Far from equilibrium, universality is identified through the scaling of the spatio-temporal evolution of the system, captured by universal exponents and functions. Theoretically, this has been studied in examples as different as the reheating process in inflationary Universe cosmology,, the dynamics of nuclear collision experiments described by quantum chromodynamics,, and the post-quench dynamics in dilute quantum gases in non-relativistic quantum field theory, , , –. However, an experimental demonstration of such scaling evolution in space and time in a quantum many-body system has been lacking. Here we observe the emergence of universal dynamics by evaluating spatially resolved spin correlations in a quasi-one-dimensional spinor Bose–Einstein condensate, , , –. For long evolution times we extract the scaling properties from the spatial correlations of the spin excitations. From this we find the dynamics to be governed by an emergent conserved quantity and the transport of spin excitations towards low momentum scales. Our results establish an important class of non-stationary systems whose dynamics is encoded in time-independent scaling exponents and functions, signalling the existence of non-thermal fixed points,,. We confirm that the non-thermal scaling phenomenon involves no fine-tuning of parameters, by preparing different initial conditions and observing the same scaling behaviour. Our analogue quantum simulation approach provides the basis with which to reveal the underlying mechanisms and characteristics of non-thermal universality classes. One may use this universality to learn, from experiments with ultracold gases, about fundamental aspects of dynamics studied in cosmology and quantum chromodynamics.