Super Efficient Absorption Filter for Quantum Memory using Atomic Ensembles in a Vapor

We demonstrate how a natural rubidium vapor cell can efficiently filter out a pump beam that produces an Raman gain in the stimulated Raman process at the D2 line of Rb. We observe a Raman gain of at least 12 dB in Rb when the pump beam is detuned below the first transition in Rb, while being exactly on-resonance with the first transition in Rb. With a single pass through a second cell, we observe an attenuation of at least 30 dB of the incoming pump at 2 mW, while the probe remained unaffected. This filtering process is critical to the realization of a single photon quantum memory based on vapor cells.