# Collective Oscillations of an Imbalanced Fermi Gas: Axial Compression Modes and Polaron Effective Mass

## TL;DR

This paper studies collective oscillations in an imbalanced Fermi gas, revealing how spin population imbalance affects hydrodynamic behavior and enabling measurement of the Fermi polaron's effective mass, aligning with theoretical predictions.

## Contribution

It provides experimental insights into the decoupling of spin component oscillations and measures the polaron effective mass in a strongly interacting Fermi gas.

## Key findings

- Hydrodynamic behavior at low polarization
- Decoupling of spin component oscillations at high imbalance
- Measured polaron effective mass as 1.17(10)

## Abstract

We investigate the low-lying compression modes of a unitary Fermi gas with imbalanced spin populations. For low polarization, the strong coupling between the two spin components leads to a hydrodynamic behavior of the cloud. For large population imbalance we observe a decoupling of the oscillations of the two spin components, giving access to the effective mass of the Fermi polaron, a quasi-particle composed of an impurity dressed by particle-hole pair excitations in a surrounding Fermi sea. We find $m^*/m=1.17(10)$, in agreement with the most recent theoretical predictions.