Temperature-Dependent Contact of Weakly Interacting Single-Component Fermi Gases and Loss Rate of Degenerate Polar Molecules

TL;DR

This paper investigates the temperature-dependent two-body loss rates in weakly interacting single-component Fermi gases, establishing a relationship with the p-wave contact and providing a unified theory that matches experimental data across various temperatures.

Contribution

It introduces a comprehensive theoretical framework connecting p-wave contact with loss rates, covering low to high temperatures without fitting parameters, applicable to both molecular and atomic Fermi gases.

Findings

Contact remains constant at low temperatures.

Contact increases quadratically with temperature initially.

Contact becomes linear at high temperatures, following the Bethe-Wigner law.

Abstract

Motivated by the experimental realization of single-component degenerate Fermi gases of polar ground state KRb molecules with intrinsic two-body losses [L. De Marco, G. Valtolina, K. Matsuda, W. G. Tobias, J. P. Covey, and J. Ye, A degenerate Fermi gas of polar molecules, Science 363, 853 (2019)], this work studies the finite-temperature loss rate of single-component Fermi gases with weak interactions. First, we establish a relationship between the two-body loss rate and the $p$-wave contact. Second, we evaluate the contact of the homogeneous system in the low-temperature regime using $p$-wave Fermi liquid theory and in the high-temperature regime using the second-order virial expansion. Third, conjecturing that there are no phase transitions between the two temperature regimes, we smoothly interpolate the results to intermediate temperatures. It is found that the contact is constant at temperatures close to zero and increases first quadratically with increasing temperature and finally -- in agreement with the Bethe-Wigner threshold law -- linearly at high temperatures. Fourth, applying the local-density approximation, we obtain the loss-rate coefficient for the harmonically trapped system, reproducing the experimental KRb loss measurements within a unified theoretical framework over a wide temperature regime without fitting parameters. Our results for the contact are not only applicable to molecular $p$-wave gases but also to atomic single-component Fermi gases, such as 40K and 6Li.