Ultrahigh and persistent optical depths of caesium in Kagom\'e-type hollow-core photonic crystal fibres

TL;DR

This paper demonstrates ultrahigh, long-lasting optical depths of caesium in Kagomé-type hollow-core photonic crystal fibres, enabling advanced light-matter interaction experiments at the single-photon level.

Contribution

It reports the first achievement of persistent optical depths exceeding 2000 for hours in a Kagomé-type fibre, significantly surpassing previous transient durations.

Findings

Transient optical depth >10^5 for up to a minute

Persistent optical depth >2000 for hours

Enables long-term quantum memory and nonlinear optics experiments

Abstract

Alkali-filled hollow-core fibres are a promising medium for investigating light-matter interactions, especially at the single-photon level, due to the tight confinement of light and high optical depths achievable by light-induced atomic desorption. However, until now these large optical depths could only be generated for seconds at most once per day, severely limiting the practicality of the technology. Here we report the generation of highest observed transient ($>10^5$ for up to a minute) and highest observed persistent ($>2000$ for hours) optical depths of alkali vapours in a light-guiding geometry to date, using a caesium-filled Kagom\'e-type hollow-core photonic crystal fibre. Our results pave the way to light-matter interaction experiments in confined geometries requiring long operation times and large atomic number densities, such as generation of single-photon-level nonlinearities and development of single photon quantum memories.