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

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 tradeoff 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 ${\ensuremath{\eta}}_{\text{e2e}}=13(2)%$, which correspond to internal memory efficiencies of ${\ensuremath{\eta}}_{\text{mem}}=33(1)%$. Simultaneously, we achieve a noise level corresponding to ${\ensuremath{\mu}}_{1}=0.07(2)$ 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.