Collective early-time spontaneous decay of a strongly driven cold atomic ensemble

TL;DR

This study investigates how a cold atomic ensemble's early-time decay rates change under strong optical driving, revealing angle-dependent superradiant and subradiant behaviors with experimental and numerical agreement.

Contribution

It provides new insights into the collective decay dynamics of strongly driven cold atoms, combining experimental and numerical analysis across different driving regimes.

Findings

Angular-dependent transition from subradiance to superradiance

Excited state population does not exhibit superradiance

Good agreement between experiment and numerical predictions

Abstract

In this work we present a numerical and experimental investigation of the collective early-time decay rates of a strongly driven and optically dense cold atomic cloud. We prepare the atomic ensemble by driving the system to its steady state with varying Rabi frequencies $\Omega$ that go from the weak $\Omega \ll \Gamma$ to the strong driving regime $\Omega \gg \Gamma$, where $\Gamma$ is the single-atom decay rate. We investigate the early-time dynamics in the transition between the strong and weak driving regimes using: i) angular-dependent observables such as the light emitted by the cloud, and ii) global observables, i.e., the excited state population. When driving the cloud on-resonance, we find that as a function of the driving frequency, the behavior of the collected light at certain angles transitions from the single-photon subradiant regime to a superradiant regime while the behavior of the excited state population does not show superradiance. The experiment shows good agreement with numerical predictions in the regime of parameters under study.