Dipole oscillations of fermionic superfluids along the BEC-BCS crossover in disordered potentials

TL;DR

This study explores how disorder affects dipole oscillations in ultracold Fermi gases across the BEC-BCS crossover, revealing disorder-dependent damping and frequency shifts that challenge existing theoretical predictions.

Contribution

The paper provides experimental and numerical analysis of disorder effects on fermionic superfluids, highlighting discrepancies between observed behavior and theoretical models across the BEC-BCS crossover.

Findings

Disorder-induced damping grows with the square of disorder strength.

Oscillation frequency shifts deviate from simple damped harmonic oscillator models.

Damping decreases with interaction strength, regardless of BEC or BCS regime.

Abstract

We investigate dipole oscillations of ultracold Fermi gases along the BEC-BCS crossover through disordered potentials. We observe a disorder-induced damping of oscillations as well as a change of the fundamental Kohn-mode frequency. The measurement results are compared to numerical density matrix renormalization group calculations as well as to a three-dimensional simulation of non-interacting fermions. Experimentally, we find a disorder-dependent damping, which grows approximately with the second power of the disorder strength. Moreover, we observe experimentally a change of oscillation frequency which deviates from the expected behavior of a damped harmonic oscillator on a percent level. While this behavior is qualitatively expected from the theoretical models used, quantitatively the experimental observations show a significantly stronger effect than predicted by theory. Furthermore, while the frequency shift seems to scale differently with interaction strength in the BEC versus BCS regime, the damping coefficient apparently decreases with the strength of interaction, but not with the sign, which changes for BEC and BCS type Fermi gases. This is surprising, as the dominant damping mechanisms are expected to be different in the two regimes.