Preparation Of Single Rydberg Excitations Via Adiabatic Passage And Creation Of Entanglement Based On Rydberg Blockade

Building long-distance quantum communication and quantum network is of great importance for the pratical use of modern quantum information technology.To acheive this goal,quantum repeaters become one of the important approaches to solve the at?tenuation problem of single photon signal in quamtum network.Among many physical systems which could be used to realize quantum repeaters,cold atomic ensembles have the advantages of long coherence time and strong collective enhancement effect.It is a system that achieves a better comprehensive index of quantum repeaters.However,the traditional DLCZ scheme still has a probabilistic defect in order to avoid high-order excitation,which greatly limits the connection efficiency between quantum nodes.we adopt the Rydberg blockade mechanism to realize deterministic preparation of single quantum states and then to manipulate it,overcoming the probabilistic defects in the original quantum repeaters scheme.Therefore,the mesoscopic cold atomic ensembles system based on Rydberg blockage becomes one of the most feasible solutions for up-grading quantum communications and quantum networks in the future.In the research of this thesis,with laser-cooling and trapping technology,first of all we construct a new experimental platform for cold Rb87 atomic ensembles,and further load the atoms in the magneto-optical trap into the optical dipole trap to pro-duce mesoscopic cold atomic ensembles,which lays the experimental foundation for introducing Rydberg blockcade mechanism and preparing single Rydberg excitation.Afterwards,we conduct a series of experimental investigations.First,in one atomic ensembles we prepare two ground state collective excitations,and perform a beam-splitter operation with Raman coupling,finally realize first Hong-Ou-Mandel(HOM)interference between inner states of Rydberg atoms,which verifys the quantum nature of collective excitations.The final state is a NOON entangled state,by employing a Ramsey interferometer procedure,we achieve a super-resolution measurement of the magnetic field,this experiment paves the way for collectively encoding and manipulat-ing more excitations in one atomic ensemble for quantum-enhanced applications.Next,by introducing momentum freedom of collective excited states,we generate semideter-ministic entanglement between the polarization of a single photon and the momentum of the remaining atomic excitation,with a measured fidelity of 0.901(8).Meanwhile,the intrinsic entanglement generation efficiency is 50%,compared with the DLCZ scheme,it is two orders of magnitude higher.The realized entanglement can be employed to create entanglement between two distant nodes in a fully heralded way and with a much higher efficiency.At last,different from the traditional two-photon Raman transition scheme for preparing single Rydberg-state excitations,we implement a new Chirp exci-tation scheme via adiabatic passage,which is more robust against variance of laser pulse duration and frequency detuning.In addition,the Chirp excitation scheme preserves in-ternal phases of the collective Rydberg excitation well,which provides another feasible solution for the preparation of a single photon source in Rydberg atomic ensembles.Our research demonstrates that the mesoscopic cold atomic ensembles system based on Rydberg blockage has strong collective enhancement feature and rich abilities to prepare entangled states deterministically,and it becomes one of the most feasible solutions for upgrading quantum communications and quantum networks in the future,and it would promote the development and application of quantum repeaters technology powerfully.