Observation of mixed singlet-triplet Rb$_2$ Rydberg molecules

TL;DR

This study uses high-resolution spectroscopy to observe and analyze mixed singlet-triplet Rb$_2$ Rydberg molecules, revealing how hyperfine interactions and magnetic fields influence their binding energies and molecular states.

Contribution

It provides the first detailed experimental observation of mixed singlet-triplet Rb$_2$ Rydberg molecules and demonstrates magnetic field tuning of their binding energies.

Findings

Effective zero-energy singlet s-wave scattering length determined.

Magnetic field tunes singlet-triplet mixing and molecular binding energies.

Calculated molecular potentials agree with experimental data.

Abstract

We present high-resolution spectroscopy of Rb$_\text{2}$ ultralong-range Rydberg molecules bound by mixed singlet-triplet electron-neutral atom scattering. The mixing of the scattering channels is a consequence of the hyperfine interaction in the ground-state atom, as predicted recently by Anderson et al. \cite{Anderson2014b}. Our experimental data enables the determination of the effective zero-energy singlet $s$-wave scattering length for Rb. We show that an external magnetic field can tune the contributions of the singlet and the triplet scattering channels and therefore the binding energies of the observed molecules. This mixing of molecular states via the magnetic field results in observed shifts of the molecular line which differ from the Zeeman shift of the asymptotic atomic states. Finally, we calculate molecular potentials using a full diagonalization approach including the $p$-wave contribution and all orders in the relative momentum $k$, and compare the obtained molecular binding energies to the experimental data.