Long-lived non-classical correlations for scalable quantum repeaters at room temperature

TL;DR

This paper demonstrates long-lived non-classical correlations in warm caesium vapour, enabling scalable room-temperature quantum repeaters by overcoming decoherence issues with motional averaging.

Contribution

It introduces a method to achieve millisecond-scale collective excitation lifetimes in warm atomic vapour, advancing room-temperature quantum repeater technology.

Findings

Achieved a collective excitation lifetime of 0.27 ms in warm caesium vapour.

Verified non-classical correlations by violating the Cauchy-Schwarz inequality.

Identified four-wave mixing noise as a key limiting factor.

Abstract

Heralded single-photon sources with on-demand readout are promising candidates for quantum repeaters enabling long-distance quantum communication. The need for scalability of such systems requires simple experimental solutions, thus favouring room-temperature systems. For quantum repeater applications, long delays between heralding and single-photon readout are crucial. Until now, this has been prevented in room-temperature atomic systems by fast decoherence due to thermal motion. Here we demonstrate efficient heralding and readout of single collective excitations created in warm caesium vapour. Using the principle of motional averaging we achieve a collective excitation lifetime of $0.27\pm 0.04$ ms, two orders of magnitude larger than previously achieved for single excitations in room-temperature sources. We experimentally verify non-classicality of the light-matter correlations by observing a violation of the Cauchy-Schwarz inequality with $R=1.4\pm 0.1>1$. Through spectral and temporal analysis we identify intrinsic four-wave mixing noise as the main contribution compromising single-photon operation of the source.