An experimental setup to generate narrowband bi-photons via four-wave mixing in cold atoms

TL;DR

This paper details an experimental setup that generates narrowband, correlated photon pairs via four-wave mixing in cold rubidium atoms, demonstrating high brightness, non-classical correlations, and potential for quantum technology applications.

Contribution

The paper introduces a novel, automated experimental setup for producing narrowband bi-photons with high spectral brightness using cold atom four-wave mixing.

Findings

Achieved a photon pair detection rate of 10^4 s^-1.

Confirmed non-classical photon correlations with a Cauchy-Schwarz violation of 5.6×10^5.

Measured a coherence time of 4.4 ns for heralded photons.

Abstract

We present our recently-built experimental setup designed to generate near-infrared and narrow-band correlated photon pairs by inducing four-wave mixing in a cold gas of $^{87}$Rb atoms confined in a magneto-optical trap. The experimental setup and its automation and control approach are described in detail. A characterization of the optical density of the atomic ensemble as well as the basic statistical measurements of the generated light are reported. The non-classical nature of the photons pairs is confirmed by observing a violation of Cauchy-Schwarz inequality by a factor of 5.6 $\times 10^5$ in a Hanbury Brown - Twiss interferometer. A $1/e$ coherence time for the heralded, idler photons of $4.4 \pm 0.1$ ns is estimated from our observations. We are able to achieve a value of $10^{4}$ s$^{-1}$ pair-detection-rate, which results in a spectral brightness of 280 (MHz s)$^{-1}$. The combination of high brightness and narrow-band spectrum makes this photon-pair source a viable tool in fundamental studies of quantum states and opens the door to use them in quantum technologies.