Rydberg-Blockade Effects in Autler-Townes Spectra of Ultracold Strontium

TL;DR

This study investigates how Rydberg interactions influence Autler-Townes spectra in ultracold strontium gases, revealing shifts, asymmetries, and broadening effects, with a combined experimental and theoretical approach highlighting the role of Rydberg blockade and decoherence.

Contribution

It introduces a novel experimental setup for two-photon Rydberg excitation in strontium and develops a density matrix model that captures interaction effects and decoherence mechanisms.

Findings

Rydberg interactions cause measurable shifts and broadening in spectra.

The density matrix model agrees with experiments for short excitation times.

Longer excitation times suggest additional dephasing mechanisms beyond standard blockade.

Abstract

We present a combined experimental and theoretical study of the effects of Rydberg interactions on Autler-Townes spectra of ultracold gases of atomic strontium. Realizing two-photon Rydberg excitation via a long-lived triplet state allows us to probe the thus far unexplored regime where Rydberg state decay presents the dominant decoherence mechanism. The effects of Rydberg interactions are observed in shifts, asymmetries, and broadening of the measured atom-loss spectra. The experiment is analyzed within a one-body density matrix approach, accounting for interaction-induced level shifts and dephasing through nonlinear terms that approximately incorporate correlations due to the Rydberg blockade. This description yields good agreement with our experimental observations for short excitation times. For longer excitation times, the loss spectrum is altered qualitatively, suggesting additional dephasing mechanisms beyond the standard blockade mechanism based on pure van der Waals interactions.