State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, People's Republic of China.
Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China.
Phys Rev Lett. 2018 Mar 23;120(12):125301. doi: 10.1103/PhysRevLett.120.125301.
We report an observation of a dynamical super Efimovian expansion in a strongly interacting Fermi gas by engineering time dependent external harmonic trap frequencies. When the trap frequency is tailored as [1/4t^{2}+1/t^{2}λlog^{2}(t/t_{})]^{1/2}, where t_{} and λ are two controllable parameters, and the change is faster than a critical value, the expansion of such a quantum gas shows novel dynamics that share the same characteristics as the super Efimov effect. A clear double-log periodicity with discrete geometric scaling emerges for the cloud size in the expansion. The universality of such scaling dynamics is verified both in the noninteracting and in the unitarity limit of Fermi gas. Moreover, the measured energy scaling reveals that the potential and internal energy also show double-log periodicity with a π/2 phase difference, but the total energy is monotonically decreased. Observing super Efimovian evolution represents a paradigm in probing universal properties and allows us in a new way to study many-body nonequilibrium dynamics with experiments.
我们通过工程学手段调控时变外部谐振陷阱频率，观察到强相互作用费米气体中的动力学超级 Efimov 膨胀。当陷阱频率被设计为[1/4t^{2}+1/t^{2}λlog^{2}(t/t_{})]^{1/2}时（其中 t_{}和 λ 是两个可调控参数，且变化速度快于一个临界值），这种量子气体的膨胀表现出与超级 Efimov 效应相同的新颖动力学。在膨胀过程中，云尺寸呈现出清晰的双对数周期性和离散的几何标度。这种标度动力学的普遍性在非相互作用和费米气体的完全简并极限中都得到了验证。此外，测量得到的能量标度揭示了势能和内能也呈现出双对数周期性，具有π/2 的相位差，但总能量单调减小。观察到超级 Efimov 演化代表了探测普遍性质的范例，使我们能够通过实验以新的方式研究多体非平衡动力学。
