Spontaneous avalanche dephasing in large Rydberg ensembles

TL;DR

This paper investigates the rapid dephasing caused by contaminant states in large Rydberg ensembles, revealing a clustered growth mechanism and proposing methods to mitigate spontaneous broadening effects.

Contribution

It provides experimental evidence of clustered growth dynamics and the reduced timescale for dephasing, along with strategies to minimize broadening in Rydberg systems.

Findings

Dephasing occurs faster than homogeneous models predict due to clustering.

The dephasing timescale scales inversely with atom number.

Stroboscopic and cryogenic techniques can help mitigate broadening.

Abstract

Strong dipole-exchange interactions due to spontaneously produced contaminant states can trigger rapid dephasing in many-body Rydberg ensembles [E. Goldschmidt et al., PRL 116, 113001 (2016)]. Such broadening has serious implications for many proposals to coherently use Rydberg interactions, particularly Rydberg dressing proposals. The dephasing arises as a runaway process where the production of the first contaminant atoms facilitates the creation of more contaminant atoms. Here we study the time dependence of this process with stroboscopic approaches. Using a pump-probe technique, we create an excess "pump" Rydberg population and probe its effect with a different "probe" Rydberg transition. We observe a reduced resonant pumping rate and an enhancement of the excitation on both sides of the transition as atoms are added to the pump state. We also observe a timescale for population growth significantly shorter than predicted by homogeneous mean-field models, as expected from a clustered growth mechanism where high-order correlations dominate the dynamics. These results support earlier works and confirm that the time scale for the onset of dephasing is reduced by a factor which scales as the inverse of the atom number. In addition, we discuss several approaches to minimize these effects of spontaneous broadening, including stroboscopic techniques and operating at cryogenic temperatures. It is challenging to avoid the unwanted broadening effects, but under some conditions they can be mitigated.