Magnetically tuned, robust and efficient filtering system for spatially multimode quantum memory in warm atomic vapors

TL;DR

This paper presents a magnetically tuned filtering system that enhances the signal-to-noise ratio in warm atomic vapor quantum memories by effectively filtering out parasitic noise while transmitting desired quantum signals.

Contribution

It introduces a novel combination of magnetically tuned absorption and Faraday filters that are insensitive to light direction, improving noise suppression in quantum memory systems.

Findings

Significant increase in signal-to-noise ratio with the filters

Effective suppression of parasitic fluorescence and four-wave mixing

Enhanced correlation measurements between Raman-scattered photons

Abstract

Warm atomic vapor quantum memories are simple and robust, yet suffer from a number of parasitic processes which produce excess noise. For operating in a single-photon regime precise filtering of the output light is essential. Here we report a combination of magnetically tuned absorption and Faraday filters, both light-direction-insensitive, which stop the driving lasers and attenuate spurious fluorescence and four-wave mixing while transmitting narrowband Stokes and anti-Stokes photons generated in write-in and readout processes. We characterize both filters with respect to adjustable working parameters. We demonstrate a significant increase in the signal to noise ratio upon applying the filters seen qualitatively in measurements of correlation between the Raman-scattered photons.