Probing a scattering resonance in Rydberg molecules with a Bose-Einstein condensate

TL;DR

This paper investigates the interaction between Rydberg atoms and a Bose-Einstein condensate, revealing how the electron-atom scattering resonance influences spectral line shapes and broadening, with implications for understanding quantum many-body systems.

Contribution

It demonstrates the role of a triplet p-wave shape resonance in Rydberg-electron scattering within a BEC, providing a microscopic model for spectral line shapes based on atom-ion interactions.

Findings

Observation of density-dependent line broadening and shape changes.

Identification of the triplet p-wave resonance's impact on interaction potentials.

Development of a microscopic model matching experimental spectra.

Abstract

We present spectroscopy of a single Rydberg atom excited within a Bose-Einstein condensate. We not only observe the density shift as discovered by Amaldi and Segre in 1934, but a line shape which changes with the principal quantum number n. The line broadening depends precisely on the interaction potential energy curves of the Rydberg electron with the neutral atom perturbers. In particular, we show the relevance of the triplet p-wave shape resonance in the Rydberg electron-Rb(5S) scattering, which significantly modifies the interaction potential. With a peak density of 5.5x10^14 cm^-3, and therefore an inter-particle spacing of 1300 a0 within a Bose-Einstein condensate, the potential energy curves can be probed at these Rydberg ion - neutral atom separations. We present a simple microscopic model for the spectroscopic line shape by treating the atoms overlapped with the Rydberg orbit as zero-velocity, uncorrelated, point-like particles, with binding energies associated with their ion-neutral separation, and good agreement is found.