Optimization and readout-noise analysis of a warm-vapor electromagnetically-induced-transparency 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 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 eta_e2e = 13(2)%, which correspond o internal memory efficiencies of eta_mem = 33(1)%. Simultaneously, we achieve a noise level corresponding to µ1 = 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.