Spectroscopy of Ultracold, Trapped Cesium Feshbach Molecules

TL;DR

This paper investigates the internal structure of ultracold Cs_2 Feshbach molecules, using magnetic and microwave spectroscopy to explore various bound states, their magnetic moments, and level crossings, advancing understanding of molecular quantum states.

Contribution

It introduces new methods for controlling and characterizing high-angular-momentum states and provides precise measurements of the binding energy of a key s-wave state in cesium molecules.

Findings

Identification of higher partial-wave states up to l=8

Precise measurement of the s-wave binding energy

Characterization of avoided level crossings via magnetic moments

Abstract

We explore the rich internal structure of Cs_2 Feshbach molecules. Pure ultracold molecular samples are prepared in a CO_2-laser trap, and a multitude of weakly bound states is populated by elaborate magnetic-field ramping techniques. Our methods use different Feshbach resonances as input ports and various internal level crossings for controlled state transfer. We populate higher partial-wave states of up to eight units of rotational angular momentum (l-wave states). We investigate the molecular structure by measurements of the magnetic moments for various states. Avoided level crossings between different molecular states are characterized through the changes in magnetic moment and by a Landau-Zener tunneling method. Based on microwave spectroscopy, we present a precise measurement of the magnetic-field dependent binding energy of the weakly bound s-wave state that is responsible for the large background scattering length of Cs. This state is of particular interest because of its quantum-halo character.