title: Observation of the Efimovian expansion in scale-invariant Fermi gases.
abstract: Scale invariance plays an important role in unitary Fermi gases. Discrete scaling symmetry manifests itself in quantum few-body systems such as the Efimov effect. Here, we report on the theoretical prediction and experimental observation of a distinct type of expansion dynamics for scale-invariant quantum gases. When the frequency of the harmonic trap holding the gas decreases continuously as the inverse of time t, the expansion of the cloud size exhibits a sequence of plateaus. The locations of these plateaus obey a discrete geometric scaling law with a controllable scale factor, and the expansion dynamics is governed by a log-periodic function. This marked expansion shares the same scaling law and mathematical description as the Efimov effect.
authors.affiliation: State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, P. R. China.
authors.forename: Shujin
authors.initials: S
authors.lastname: Deng
authors.affiliation: Institute for Advanced Study, Tsinghua University, Beijing 100084, P. R. China.
authors.forename: Zhe-Yu
authors.initials: ZY
authors.lastname: Shi
authors.affiliation: State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, P. R. China.
authors.forename: Pengpeng
authors.initials: P
authors.lastname: Diao
authors.affiliation: State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, P. R. China.
authors.forename: Qianli
authors.initials: Q
authors.lastname: Yu
authors.affiliation: Institute for Advanced Study, Tsinghua University, Beijing 100084, P. R. China.
authors.forename: Hui
authors.initials: H
authors.lastname: Zhai
authors.affiliation: Department of Physics, Renmin University of China, Beijing 100872, P. R. China. qiran@ruc.edu.cn hbwu@phy.ecnu.edu.cn.
authors.forename: Ran
authors.initials: R
authors.lastname: Qi
authors.affiliation: State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, P. R. China. Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China. qiran@ruc.edu.cn hbwu@phy.ecnu.edu.cn.
authors.forename: Haibin
authors.initials: H
authors.lastname: Wu