Study of the Electromagnetically Induced Transparency in a cold atomic ensemble and application to quantum memories - Lambert Giner

In order to implement quantum communications, such as quantum cryptography, over distances larger than one hundred of kilometers using optical fibers, it is required to develop new tools know as "quantum repeaters". The way those devices work is based on the development of quantum memories which that store the quantum state of light and to retrieve it on demand. This talk presents the realization of a quantum memory based on a cold atomic ensemble of cesium using a protocol based on Electromagnetically Induced Transparency (EIT). The first part of this talk describes the realization of a magneto - optical trap producing a cold atomic cloud of cesium exhibiting a large optical depth. The second part explains the study of the transparency of the media. Indeed, in a Ë energy scheme, the application of a control field on the nearby transition of the signal field results in opening a transparency window. Two phenomena can explain this observation: the EIT which corresponds to destructive interferences between various excitation paths and Autler - Townes Splitting (ATS) corresponding to the separation of the excited state into two dressed states. A quantitative and detailed study has been carried out. The last part shows the demonstration of the storage of a coherent state in the single photon regime with an efficiency of 24% and the storage of a quantum information bit encoded into the orbital momentum of light results in the single photon regime with a fidelity larger than 92%