Preparation And Manipulation Of Single Quantum States In An Atomic Ensemble Based On Rydberg Blockade Mechanism

Realizing large-scale quantum communication and quantum network is one of the most significant researches among quantum information technology applications,in which quantum repeaters play an important role.Cold atomic ensembles are promising physical systems for building quantum repeating systems.However,current schemes utilizing atomic ensembles suffer a drawback of probability.By introducing Rydberg blockade mechanism,we can overcome this shortcoming of ensembles,and realize de-terministic preparation and manipulation of single quantum states and entangled states,which will promote the development of quantum repeater technology.Combining the results in traditional quantum memory research with probabilistic sources with those in manipulation of Rydberg atoms and Rydberg blockade effect in atomic ensembles,we construct a new experimental platform for quantum information processing using Rydberg atoms,and we accomplish a series of work for related explo-rations and researches.We first solve the most critical technical problems.For instance,we produce a mesoscopic atomic ensemble successfully and lock the lasers with very narrow linewidths.Then by using electromagnetically induced transparency with Ry-dberg states,we realize Rydberg state manipulation and observe the nonlinear effect induced by strong Rydberg interactions.Next,in the mesoscopic atomic ensemble,we realize Rydberg blockade and also coherent manipulation of single Rydberg excitations,so we create single Rydberg-state excitations and single ground-state excitations deter-ministically.Furthermore,utilizing Rydberg blockade,we prepare two ground state collective excitations in one atomic ensemble,and realize Hong-Ou-Mandel interfer-ence between them by stimulated Raman coupling.This result not only lays the foun-dation for deterministic preparation of entanglement between photons and atomic quan-tum memories,but also is the experimental beginning of many-qubit encoding scheme in one ensemble.At last,using the dynamical evolution of two collective excitations under Rydberg blockade mechanism,together with the interference effect during the read-out process,we successfully generate entanglement between atomic ensembles and photons,with an intrinsic efficiency of 50%.Compared with previous probabilistic schemes for entanglement generation,the effeciency here is increased by two orders of magnitude,which will be of great importance in quantum repeater applications.Mesoscopic cold atomic ensembles based on Rydberg blockade possess the ad-vantage of atomic ensembles with collective enhancement feature,together with the advantage of single particles for deterministic quantum state preparation and manip-ulation.Hence they will have a bright application prospect in quantum information processing.We believe that the " Rydberg type" quantum repeater,integrated with optical lattice and cavity technology,is a brilliant solution for efficient and practical quantum repeaters in the future.