Probing a quantum gas with single Rydberg atoms

TL;DR

This paper introduces a new spectroscopic technique using Rydberg states to measure and spatially resolve the density of quantum gases, and to monitor phase transitions like BEC formation.

Contribution

The authors develop a novel method leveraging Rydberg state energy shifts for in-situ density measurement and spatial localization in quantum gases.

Findings

Achieved spatial resolution below optical wavelengths for density shells.

Successfully measured mean density using Rydberg spectroscopy.

Monitored the phase transition from thermal gas to BEC.

Abstract

We present a novel spectroscopic method for probing the \insitu~density of quantum gases. We exploit the density-dependent energy shift of highly excited {Rydberg} states, which is of the order $10$\MHz\,/\,1E14\,cm$^{\text{-3}}$ for \rubidium~for triplet s-wave scattering. The energy shift combined with a density gradient can be used to localize Rydberg atoms in density shells with a spatial resolution less than optical wavelengths, as demonstrated by scanning the excitation laser spatially across the density distribution. We use this Rydberg spectroscopy to measure the mean density addressed by the Rydberg excitation lasers, and to monitor the phase transition from a thermal gas to a Bose-Einstein condensate (BEC).