Coherent Control Of The Spinwave In Cold Atomic Quantum Memory And Creation Of The Quantum Degenerate Bose-Fermi Mixture Gas

Quantum memory is an important element for quantum information process-ing applications, i.e., quantum network, quantum repeater and quantum com-puting. The quantum memory based on cold atomic ensembles is superior over other systems in terms of the overall performance nowadays, where many impor-tant progresses have been made so far. To make the quantum memory one step closer to a universal system, the direct coherent manipulations of the memory are essential.This thesis mainly consists of two different parts. The first part is about the studies on coherent manipulations of the single-quanta spin-waves in the cold atomic ensemble quantum memory. In this part, we have shown how to eliminate the motional dephasing of spin-waves with a Raman rephasing scheme, which finally for the first time demonstrates the feasibility of harnessing the spin echo method to extend the lifetime of ensemble-based quantum memories at the single-quanta level, where there have been theoretical disputes before. Besides, we have also realized the arbitrary rotations and single-qubit-gate operations on the spin-wave qubit, with stimulated Raman transitions and Larmor precessions, where the measured operations feature with both high state fidelities and high process fidelities. Thirdly, with the two-photon Raman transitions driven by a standing wave light field, we have demonstrated an improvement of nine times in the fi-nal resolution of atom pattern preparations compared with the optical diffraction limit of standing waves, which thus provides a proof-of-principle demonstration of one recently reported quantum lithography scheme.The second part of the thesis introduces the construction of an ultracold atomic apparatus, which is capable of laser cooling and trapping of both Sodium and Potassium atoms, and creating the quantum degenerate Bose-Fermi mixture gases. In our experiment, the typical atom numbers of the Na23 BEC and K40 Fermi gas are around 0.1 million, and the temperature of the Potassium atoms is about 0.4 to 0.5 of the Fermi temperature. The degenerate mixture realized here brings us to the new start point for pursuing ultracold heteronucluear Feshbach molecules and the final absolute rovibrational ground state polar molecules with optical STIRAP processes.