Optimization and readout-noise analysis of a warm vapor EIT memory on the Cs D1 line

Abstract: Quantum memories promise to enable global quantum repeater networks. For field applications, alkali metal vapors constitute an exceptional storage platform, as neither cryogenics, nor strong magnetic fields are required. We demonstrate a technologically simple, in principle satellite-suited quantum memory based on electromagnetically induced transparency on the cesium D1 line, and focus on the trade-off between end-to-end efficiency and signal-to-noise ratio, both being key parameters in applications. For coherent pulses containing one photon on average, we achieve storage and retrieval with end-to-end efficiencies of $\eta_{e2e} = 13(2)\%$, which correspond to internal memory efficiencies of $\eta_{mem} = 33(1)\%$. Simultaneously, we achieve a noise level corresponding to $\mu_1 = 0.07(2)$ signal photons. This noise is dominated by spontaneous Raman scattering, with contributions from fluorescence. Four wave mixing noise is negligible, allowing for further minimization of the total noise level.