A Simple and Efficient Absorption Filter for Single Photons from a Cold Atom Quantum Memory

TL;DR

This paper presents a simple, passive vapor cell filter that significantly reduces noise in single-photon signals from a cold atom quantum memory, enhancing its efficiency and non-classical correlations.

Contribution

The authors demonstrate a novel, efficient absorption filter using a vapor cell that improves quantum memory performance by reducing noise without substantial photon loss.

Findings

Attenuates residual laser light and noise photons by nearly two orders of magnitude.

Increases quantum memory readout efficiency by approximately 35%.

Provides 18 dB attenuation of pump laser and spontaneous emission noise per 1 dB photon loss.

Abstract

The ability to filter unwanted light signals is critical to the operation of quantum memories based on neutral atom ensembles. Here we demonstrate an efficient frequency filter which uses a vapor cell filled with $^{85}$Rb and a buffer gas to attenuate both residual laser light and noise photons by nearly two orders of magnitude with little loss to the single photons associated with our cold $^{87}$Rb quantum memory. This simple, passive filter provides an additional 18 dB attenuation of our pump laser and erroneous spontaneous emissions for every 1 dB loss of the single photon signal. We show that the addition of a frequency filter increases the non-classical correlations and readout efficiency of our quantum memory by $\approx35\%$.