From molecular spectra to a density shift in dense Rydberg gases.

T Pfau,A Gaj,J B Balewski,A T Krupp,R Löw,S Hofferberth

doi:10.1038/ncomms5546

Abstract

In Rydberg atoms, at least one electron is excited to a state with a high principal quantum number. In an ultracold environment, this low-energy electron can scatter off a ground state atom allowing for the formation of a Rydberg molecule consisting of one Rydberg atom and several ground state atoms. Here we investigate those Rydberg molecules created by photoassociation for the spherically symmetric S-states. A step by step increase of the principal quantum number up to n=111 enables us to go beyond the previously observed dimer and trimer states up to a molecule, where four ground state atoms are bound by one Rydberg atom. The increase of bound atoms and the decreasing binding potential per atom with principal quantum number results finally in an overlap of spectral lines. The associated density-dependent line broadening sets a fundamental limit, for example, for the optical thickness per blockade volume in Rydberg quantum optics experiments.

Highlights

In Rydberg atoms, at least one electron is excited to a state with a high principal quantum number
For low principal quantum numbers clearly distinguishable molecular lines are present on the red side of the atomic peak, which is situated at the origin
The densitydependent dephasing resulting from the existence of many molecular lines within the Rydberg line envelope sets a fundamental limit for the number of atoms inside the blockade radius, that is, the optical thickness, for n480

Summary

Introduction

In Rydberg atoms, at least one electron is excited to a state with a high principal quantum number. This low-energy electron can scatter off a ground state atom allowing for the formation of a Rydberg molecule consisting of one Rydberg atom and several ground state atoms. 1, show very weak binding energies, similar to magneto-associated Feshbach molecules[2,3], and require ultracold temperatures. The bond in these molecules results from the scattering of a slow Rydberg electron from a neutral atom with a negative scattering length a The singlet scattering length is positive and does not lead to a bound state

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Results

Conclusion