High efficiency Raman memory by suppressing radiation trapping

S E Thomas,A Feizpour,J Nunn,I A Walmsley,J H D Munns,C Qiu,D J Saunders,B Brecht,P M Ledingham,K T Kaczmarek

doi:10.1088/1367-2630/aa7534

S E Thomas, A Feizpour + Show 8 more

Open Access

https://doi.org/10.1088/1367-2630/aa7534

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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 in caesium vapour at high optical depths of up to 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.

Highlights

The strong spin-orbit coupling in alkali vapours enables a broadband optical interface for spin coherence via Raman scattering
Dense alkali vapours can serve as a frequency reference for atomic clocks and magnetometry [1, 2], a buffer in optical signal processing [3], and in the quantum domain, provide a source of squeezed light via four-wave mixing [4, 5] or a medium for storing and synchronising photons, via the Raman- and DLCZ-type quantum memory protocols [6,7,8,9,10,11,12,13,14,15]
Very high atomic densities can be achieved without complex atom trapping by heating a vapour cell, but in vapour cell systems the ability to spin-polarise the ensemble by optical pumping [16] is hampered by radiation trapping at high densities [17]

Summary

INTRODUCTION

The strong spin-orbit coupling in alkali vapours enables a broadband optical interface for spin coherence via Raman scattering. Dense alkali vapours can serve as a frequency reference for atomic clocks and magnetometry [1, 2], a buffer in optical signal processing [3], and in the quantum domain, provide a source of squeezed light via four-wave mixing [4, 5] or a medium for storing and synchronising photons, via the Raman- and DLCZ-type quantum memory protocols [6,7,8,9,10,11,12,13,14,15] In each of these examples, the desired light-matter coupling is a collective effect, where the coupling strength scales favourably with the optical depth d, which is proportional to the atomic density. We use this system to demonstrate efficient light storage with very high and controllable gain, and these results demonstrate a route towards high efficiency storage of non-classical light

OPTICAL PUMPING IN ALKALI VAPOURS

Findings

RAMAN MEMORY