Optimization and noise study of a warm vapor EIT memory on the Cs D1 line

Abstract

Quantum memories are a key element for the realisation of quantum repeaters, essential for long-distance quantum communication. Especially for satellite-based quantum networks, alkali metal vapours constitute an excellent storage platform, as neither cryogenics, nor strong magnetic fields are required. We have realised a technologically simple, in principle satellite-suited quantum memory in Caesium vapor, based on electromagnetically induced transparency (EIT) on the Cs D1 line. We focus on the simultaneous optimization of end-to-end efficiency and signal-to-noise level in the memory, which will make our system suitable for many different applications. We have achieved light storage at the single-photon level with end-to-end efficiencies up to 12%, which correspond to internal memory efficiencies of up to 30%. Simultaneously we achieve a minimal noise level corresponding to µ_1=0.029 signal photons. Furthermore, we have determined the limiting noise source at this level to be four-wave mixing noise in the Lambda-system and present solutions to minimise this read-out noise.