Collective radiative dynamics of an ensemble of cold atoms coupled to an optical waveguide

TL;DR

This study explores the collective radiative behavior of cold atoms coupled to an optical nanofiber, revealing superradiance and directional effects through experimental and theoretical analysis of light transmission and decay dynamics.

Contribution

It provides new insights into the microscopic dynamics and directional superradiant effects in cold atom ensembles coupled to nanophotonic waveguides.

Findings

Superradiant decay faster than single-atom rate in forward direction

No decay speed-up observed in backward direction

Progressive build-up of collective response demonstrated

Abstract

We experimentally and theoretically investigate collective radiative effects in an ensemble of cold atoms coupled to a single-mode optical nanofiber. Our analysis unveils the microscopic dynamics of the system, showing that collective interactions between the atoms and a single guided photon gradually build-up along the atomic array in the direction of propagation of light. These results are supported by time-resolved measurements of the light transmitted and reflected by the ensemble after excitation via nanofiber-guided laser pulses, whose rise and fall times are shorter than the atomic lifetime. Superradiant decays more than one order of magnitude faster than the single-atom free-space decay rate are observed for emission in the forward-propagating guided mode, while at the same time no speed-up of the decay rate are measured in the backward direction. In addition, position-resolved measurements of the light that is transmitted past the atoms are performed by inserting the nanofiber-coupled atomic array in a 45-m long fiber ring-resonator, which allow us to experimentally reveal the progressive growth of the collective response of the atomic ensemble. Our results highlight the unique opportunities offered by nanophotonic cold atom systems for the experimental investigation of collective light-matter interaction.