Radio-Frequency Spectroscopy of Ultracold Fermions

TL;DR

This paper uses radio-frequency spectroscopy to investigate ultracold fermions, revealing the absence of mean-field clock shifts due to fermionic antisymmetry and exploring interaction effects near the quantum unitarity limit.

Contribution

It provides new insights into the interaction-induced resonance shifts and their suppression in strongly interacting regimes of ultracold fermionic gases.

Findings

No mean-field clock shifts observed, confirming fermionic antisymmetry effects.

Resonance shifts proportional to interaction strengths in three-level systems.

Suppression of shifts in the strongly interacting regime, indicating many-body effects.

Abstract

Radio-frequency techniques were used to study ultracold fermions. We observed the absence of mean-field "clock" shifts, the dominant source of systematic error in current atomic clocks based on bosonic atoms. This is a direct consequence of fermionic antisymmetry. Resonance shifts proportional to interaction strengths were observed in a three-level system. However, in the strongly interacting regime, these shifts became very small, reflecting the quantum unitarity limit and many-body effects. This insight into an interacting Fermi gas is relevant for the quest to observe superfluidity in this system.