Decoherence of Impurities in a Fermi Sea of Ultracold Atoms

TL;DR

This study measures how impurities in a Fermi sea lose coherence depending on interaction strength and temperature, revealing Fermi liquid behavior at weak interactions and non-Fermi liquid effects at strong interactions.

Contribution

It provides experimental insights into impurity decoherence in ultracold Fermi gases, highlighting the transition from Fermi liquid to non-Fermi liquid behavior across a Feshbach resonance.

Findings

Decoherence rates match Fermi liquid theory at weak interactions.

Strong interactions cause temperature-independent decoherence enhancement.

Behavior beyond Fermi liquid theory observed at strong coupling.

Abstract

We investigate the decoherence of $^{40}$K impurities interacting with a three-dimensional Fermi sea of $^{6}$Li across an interspecies Feshbach resonance. The decoherence is measured as a function of the interaction strength and temperature using a spin-echo atom interferometry method. For weak to moderate interaction strengths, we interpret our measurements in terms of scattering of K quasiparticles by the Fermi sea and find very good agreement with a Fermi liquid calculation. For strong interactions, we observe significant enhancement of the decoherence rate, which is largely independent of temperature, pointing to behavior that is beyond the Fermi liquid picture.