Steady-state, cavity-less, multimode superradiance in a cold vapor

TL;DR

This paper reports the experimental realization of steady-state, cavity-less superradiance in a cold vapor, where a self-organized density grating leads to intense, nearly coherent optical emission with long coherence times, useful for quantum information.

Contribution

It demonstrates a novel steady-state superradiance mechanism in a cold vapor without cavities, including experimental mapping and theoretical modeling of the phase transition boundary.

Findings

Superradiant emission persists for several seconds.

A density grating forms above a critical pump intensity.

The superradiance exhibits strong temporal correlations.

Abstract

We demonstrate steady-state, mirrorless superradiance in a cold vapor pumped by weak optical fields. Beyond a critical pump intensity of 1 mW/cm$^2$, the vapor spontaneously transforms into a spatially self-organized state: a density grating forms. Scattering of the pump beams off this grating generates a pair of new, intense optical fields that act back on the vapor to enhance the atomic organization. We map out experimentally the superradiant phase transition boundary and show that it is well-described by our theoretical model. The resulting superradiant emission is nearly coherent, persists for several seconds, displays strong temporal correlations between the various modes, and has a coherence time of several hundred $\mu$s. This system therefore has applications in fundamental studies of many-body physics with long-range interactions as well as all-optical and quantum information processing.