Optical quantum memories are essential for quantum communications and photonic quantum technologies.Ensemble optical memories based on 3-level interactions Wheel Spacer are a popular basis for implementing these memories.All such memories, however, suffer from loss due to scattering.In off-resonant 3-level interactions, such as the Raman gradient echo memory (GEM), scattering loss can be reduced by a large detuning from the intermediate state.
In this work, we show how electromagnetically induced transparency adjacent to the Raman absorption line plays a crucial role in reducing scattering loss, so that maximum efficiency is in fact achieved at a moderate detuning.Furthermore, the effectiveness of the transparency, and therefore the efficiency of GEM, depends on the order in which gradients are applied to store and recall the light.We provide a theoretical analysis and show experimentally Complete Skateboards how the efficiency depends on gradient order and detuning.