High Efficiency Raman Memory by Suppressing Radiation Trapping

TL;DR

This paper demonstrates a highly efficient Raman memory in alkali vapours by employing quenching with molecular buffer gas to suppress radiation trapping, achieving near-perfect spin-polarisation at high optical depths for improved light storage.

Contribution

It introduces a quenching technique with molecular buffer gas to significantly enhance spin-polarisation and optical depth in alkali vapours, enabling more efficient GHz-bandwidth Raman memory.

Findings

Achieved over 99.5% spin-polarisation in caesium vapour.

Reached optical depths up to approximately 2 x 10^5, four times higher than without quenching.

Enabled efficient light storage with high gain in a GHz bandwidth Raman memory.

Abstract

Raman interactions in alkali vapours are used in applications such as atomic clocks, optical signal processing, generation of squeezed light and Raman quantum memories for temporal multiplexing. To achieve a strong interaction the alkali ensemble needs both a large optical depth and a high level of spin-polarisation. We implement a technique known as quenching using a molecular buffer gas which allows near-perfect spin-polarisation of over $99.5\%$ in caesium vapour at high optical depths of up to $\sim 2 \times 10^5$; a factor of 4 higher than can be achieved without quenching. We use this system to explore efficient light storage with high gain in a GHz bandwidth Raman memory.