Motion-induced directionality of collective emission in a non-chiral waveguide

TL;DR

This paper demonstrates how thermal motion and Raman-induced phases can induce controllable directionality in collective emission from atoms in a non-chiral waveguide, with potential for nonreciprocal interactions.

Contribution

It introduces a method to achieve and control emission directionality in non-chiral waveguides using Raman processes and atomic motion, supported by numerical simulations and a simple theoretical model.

Findings

Achieved up to 89% emission directionality.

Observed coherence buildup in superfluorescent bursts.

Modeled directionality through thermal motion effects.

Abstract

We report on the observation of motion-induced directionality in the collective emission of atoms confined within a hollow-core waveguide. Unlike in chiral waveguides, the atom-field coupling is here isotropic in the forward and backward direction. However, Raman-induced effective two-level emitters with spatially oscillating phases of the transition dipole enable thermally induced, but controllable directionality of the collective emission. By tuning the characteristic rate of collective decay we achieve a directionality of up to 0.89(1). We furthermore study the correlations of the emitted light close to and well above the threshold to collective emission, showing a buildup of coherence in the superfluorescent bursts while exhibiting thermal statistics below the threshold. To understand the underlying mechanism we employ numerical simulations based on the Truncated Wigner Approximation for spins and find good agreement. Additionally we present a simple model capable of reproducing the observed directionality via location blurring induced by the thermal motion of the atoms during collective emission. Our results will enable studies of collective, nonreciprocal interactions in non-chiral systems.