Ultrabright and narrowband intra-fiber biphoton source at ultralow pump power

TL;DR

This paper presents a highly bright, narrowband, nonclassical photon pair source using cold atoms in a hollow-core fiber, achieving ultralow pump power operation suitable for quantum communication and heralded single-photon generation.

Contribution

The study demonstrates a novel ultrabright, narrowband intra-fiber biphoton source with record spectral brightness at ultralow pump powers, combining atomic ensembles and waveguide technology.

Findings

Achieved spectral brightness up to 2×10^9 pairs/(s MHz mW) at pump powers below 100 nW.

Observed nonclassical correlations and heralded single-photon operation.

Approached the limit where photon pairs overlap in time, indicating high source brightness.

Abstract

Nonclassical photon sources of high brightness are key components of quantum communication technologies. We here demonstrate the generation of narrowband, nonclassical photon pairs by employing spontaneous four-wave mixing in an optically-dense ensemble of cold atoms within a hollow-core fiber. The brightness of our source approaches the limit of achievable generated spectral brightness at which successive photon pairs start to overlap in time. For a generated spectral brightness per pump power of up to $2\times 10^{9} \ \textrm{pairs/(s MHz mW)}$ we observe nonclassical correlations at pump powers below $100 \textrm{nW}$ and a narrow bandwidth of $2\pi\times 6.5 \ \textrm{MHz}$. In this regime we demonstrate that our source can be used as a heralded single-photon source. By further increasing the brightness we enter the regime where successive photon pairs start to overlap in time and the cross-correlation approaches a limit corresponding to thermal statistics. Our approach of combining the advantages of atomic ensembles and waveguide environments is an important step towards photonic quantum networks of ensemble based elements.