Ultrafast many-body dynamics of dense Rydberg gases and ultracold plasma

TL;DR

This study explores the ultrafast many-body dynamics in dense Rydberg gases and ultracold plasmas created in a Bose-Einstein condensate, revealing how laser tuning influences the formation pathways and electron energy distributions.

Contribution

It demonstrates control over initial states leading to Rydberg gases or ultracold plasmas by tuning laser wavelength and validates molecular dynamics simulations with experimental data.

Findings

Good agreement between simulations and experiments on electron distributions

Charge imbalance identified as key factor in Rydberg gas decay

Large bandwidth laser overcomes Rydberg blockade constraints

Abstract

Understanding Coulomb driven many-body dynamics in ultracold atomic systems far from equilibrium remains an open challenge, particularly when ultrafast excitation channels create competing pathways toward Rydberg gases or ultracold plasmas. Here, we investigate the many-body dynamics in a $^{87}$Rb Bose-Einstein condensate after exposure to a single femtosecond laser pulse. By tuning the laser wavelength across the two-photon ionization threshold, we can control the initial state that is either dominated by free electrons and leads to an ultracold plasma or dominated by electrons in excited states which leads to a dense Rydberg gas. The large bandwidth enables overcoming the Rydberg blockade that limits the excitation density for narrow-linewidth lasers. We directly measure the kinetic energy of the released electrons and compare the final distribution of free, bound and plasma electrons to molecular dynamics simulations where the electrons are modeled as individual particles including collisional ionization and recombination processes. We find very good agreement between the simulated electron distribution and the experimental observation. We identify charge imbalance as main driver for the decay of a dense Rydberg gas into an ultracold plasma.