Observation of the Efimovian Expansion in Scale Invariant Fermi Gases

TL;DR

This paper reports the first experimental observation of a novel expansion dynamics in scale invariant Fermi gases, exhibiting discrete scaling laws and log-periodic behavior similar to the Efimov effect, revealing underlying symmetries.

Contribution

It introduces a new type of expansion dynamics in quantum gases with discrete scaling symmetry, combining theoretical prediction and experimental validation.

Findings

Observation of expansion plateaus obeying geometric scaling

Expansion dynamics governed by a log-periodic function

Demonstration of temporal discrete scaling symmetry in quantum gases

Abstract

Scale invariance emerges and plays an important role in strongly correlated many-body systems such as critical regimes nearby phase transitions and the unitary Fermi gases. Discrete scaling symmetry also manifests itself in quantum few-body systems such as the Efimov effect. Here we report both theoretical predication and experimental observation of a novel type expansion dynamics for scale invariant quantum gases. When the frequency of the harmonic trap holding the gas decreases continuously as the inverse of time $t$, surprisingly, the expansion of cloud size exhibits a sequence of plateaus. Remarkably, the locations of these plateaus obey a discrete geometric scaling law with a controllable scale factor and the entire expansion dynamics is governed by a log-periodic function. This striking expansion of quantum Fermi gases shares similar scaling laws and same mathematical description as the Efimov effect. Our work demonstrates the first expansion dynamics of a quantum many-body system with the temporal discrete scaling symmetry, which reveals the underlying spatial continuous scaling symmetry of the many-body system.