Feshbach resonances in Cesium at Ultra-low Static Magnetic Fields

TL;DR

This paper reports the observation and theoretical analysis of Feshbach resonances in cesium atoms at ultra-low magnetic fields using an atomic fountain clock, revealing detailed resonance structures and collisional dynamics.

Contribution

It presents the first observation of cesium Feshbach resonances at ultra-low fields and provides a coupled-channels model that accurately describes these resonances and their asymmetric shapes.

Findings

Feshbach resonances observed at ultra-low magnetic fields in cesium.

Resonances are identified as s-wave involving weakly-bound triplet states.

Theoretical calculations match experimental data with high accuracy.

Abstract

We have observed Feshbach resonances for 133Cs atoms in two different hyperfine states at ultra-low static magnetic fields by using an atomic fountain clock. The extreme sensitivity of our setup allows for high signal-to-noise-ratio observations at densities of only 2*10^7 cm^{-3}. We have reproduced these resonances using coupled-channels calculations which are in excellent agreement with our measurements. We justify that these are s-wave resonances involving weakly-bound states of the triplet molecular Hamiltonian, identify the resonant closed channels, and explain the observed multi-peak structure. We also describe a model which precisely accounts for the collisional processes in the fountain and which explains the asymmetric shape of the observed Feshbach resonances in the regime where the kinetic energy dominates over the coupling strength.