Atomic quantum memory for photon polarization

Abstract

Using an ensemble of ultracold Cesium atoms in an optical cavity we demonstrate the efficient storage and retrieval of quantum information in the form of single photons. We use a photon that has scattered into the cavity mode to herald a successful creation of a collective excitation of Cesium atoms and hence our ability to retrieve a photon from the stored excitation at a later time. Post-selecting out only data that was preceded by a heralding photon we have achieved single-photon recovery efficiencies as high as 84%. We construct an atomic quantum memory for arbitrary optical polarization states using this technique on two spatially overlapped atomic samples. The two samples constitute a quantum memory making use of a bijective mapping between a photon polarization and a shared collective excitation in the atoms. The stored state is later retrieved as a single-photon polarization state. This memory showed an average fidelity of 0.93(5) for the recovered fiducial states as well as a conditional autocorrelation function g2 = 0.24(6), indicating the single-photon nature of the retrieved photons. In this thesis, a general discussion of the techniques employed and their background theory will be given, followed by a more detailed explanation of this most recent experiment.