Density and temperature dependence of breathing-mode damping

Determine whether the normalized breathing-mode damping rate Γ_B/ω_B increases with atomic density and temperature in an isotropically trapped unitary Fermi gas, resolving the current inconclusiveness caused by the large uncertainty in the dipole-mode damping rate used to assess technical fluctuations.

Background

The paper measures the breathing mode of a unitary Fermi gas in an isotropic trap and finds a very small normalized damping rate Γ_B/ω_B ≈ 0.002 with frequency ω_B ≈ 2ω_0, demonstrating the robustness of SO(2,1) symmetry. The authors analyze possible sources of residual damping, including trap asphericity, anharmonicity, bulk viscosity, and technical fluctuations, and estimate these contributions using hydrodynamic theory and auxiliary measurements (e.g., dipole and quadrupole modes).

While presenting damping data across different densities and temperatures (Fig. 5), the authors note an apparent increase of Γ_B/ω_B with density and temperature but explicitly state that they cannot draw concrete conclusions due to the large uncertainty in the dipole-mode damping rate, which they use as a proxy for technical fluctuations. Clarifying the actual dependence of Γ_B/ω_B on density and temperature remains necessary to fully characterize residual damping under SO(2,1) symmetry.