Quantum memory for light via a stimulated off-resonant Raman process: Beyond the three-level<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>Λ</mml:mi></mml:mrow></mml:math>-scheme approximation

Abstract

We consider a quantum memory scheme based on the conversion of a signal pulse into a long-lived spin coherence via stimulated off-resonant Raman process. For a storing medium consisting of alkali-metal atoms, we have calculated the Autler-Townes resonance structure created by a strong control field. By taking into account the upper hyperfine states of the ${D}_{1}$ optical transition, we show important deviations from the predictions of the usual three-level $\ensuremath{\Lambda}$-scheme approximation and we demonstrate an enhancement of the process for particular detunings of the control. We estimate the memory efficiency one can obtain using this configuration.