Direct Observation of Resonant Scattering Phase Shifts and their Energy Dependence

TL;DR

This study directly measures how the scattering phase shifts of cesium atoms vary with energy, revealing detailed Feshbach resonance behavior that can improve understanding of atomic interactions and fundamental constants.

Contribution

It provides the first direct observation of energy-dependent scattering phase shifts in cesium atoms, resolving overlapping resonances at threshold.

Findings

Resolved overlapping Feshbach resonances at threshold

Measured rapid variation of scattering phase shifts

Achieved phase uncertainty of 8 mrad

Abstract

We scan the collision energy of two clouds of cesium atoms between 12 and 50 $\mu$K in atomic fountain clock. By directly detecting the difference of s-wave scattering phase shifts, we observe a rapid variation of a scattering phase shift through a series of Feshbach resonances. At the energies we use, resonances that overlap at threshold become resolved. Our statistical phase uncertainty of 8 mrad can be improved in future precision measurements of Feshbach resonances to accurately determine the Cs-Cs interactions, which may provide stringent limits on the time variation of fundamental constants.