Persistent breather and dynamical symmetry in a unitary Fermi gas

TL;DR

This paper reports the experimental observation of a long-lived, persistent breathing mode in a 3D unitary Fermi gas, demonstrating the protection of dynamical symmetry by SO(2,1) in a strongly interacting quantum system.

Contribution

The study experimentally realizes a nearly perfect SO(2,1) symmetry in a 3D unitary Fermi gas, enabling persistent breathing oscillations and advancing understanding of many-body non-equilibrium dynamics.

Findings

Breathing mode oscillates at twice the trap frequency.

Damping rate is extremely low, ratio to oscillation frequency is 0.002.

Oscillation properties are robust across different densities and temperatures.

Abstract

SO(2,1) dynamical symmetry makes a remarkable prediction that the breathing oscillation of a scale invariant quantum gas in an isotropic harmonic trap is isentropic and can persist indefinitely. In 2D, this symmetry is broken due to quantum anomaly in the strongly interacting range, and consequently the lifetime of the breathing mode becomes finite. The persistent breather in a strongly interacting system has so far not been realized. Here we experimentally achieve the long-lived breathing mode in a 3D unitary Fermi gas, which is protected by the SO(2,1) symmetry. The nearly perfect SO(2,1) symmetry is realized by loading the ultracold Fermi gas in an isotropic trap and tuning the interatomic interaction to resonance. The breathing mode oscillates at twice the trapping frequency even for large excitation amplitudes. The ratio of damping rate to oscillation frequency is as small as 0.002, providing an interacting persistent breather. The oscillation frequency and damping rate keep nearly constant for different atomic densities and temperatures, demonstrating the robustness of the SO(2,1) symmetry in 3D. The factors that lead to the residual damping have also been clarified. This work opens the way to study many-body non-equilibrium dynamics related to the dynamical symmetry.