The Generation Of Entanglement State And The Implementation Of SWAP Gate Base On Dipole Blockade Mechanism And Atomic Ensembles System

The combination of information science and quantum mechanics make a new subject, which can implement many tasks that are not completed with classical information theory. Quantum information science includes quantum computing, quantum cryptography, quantum communication, and et al.. In quantum information science, quantum entanglement is a valuably important concept,. Especially, multiqubit entangled state (such as the W state, GHZ state, and Cluster state) is an important physical resources for realizing quantum information processing. The quantum logic gate is a key component for realizing quantum computing and quantum communication.Rydberg atomic ensemble, as an important physical realization system in quantum information processing, plays an increasingly important role in quantum information science due to its wonderful physical properties and collective enhancement. Therefore, the researches on the preparation of multiqubit entangled state and construction of quantum logic gate have importantly theoretical and practical significance. The main work is listed below:1,Generation of GHZ state and cluster state with atomic ensembles via the dipole blockade mechanism. First, we propose a scalable scheme to generate the n-qubit GHZ state base on the dipole-dipole interaction between two adjacently atomic ensembles. Then, we propose a scalable scheme to generate the n-qubit cluster state. Compared with the previous protocols, our scheme need only classical light replacing single-photon source,, which further reduces experimental difficulties. The determinate creation of multiqubit entangled state in our scheme would be more efficient than the probabilistic generation, and this efficiency would become even more significant with an increasing number of the qubits involved. Hence, our proposals open up a prospect to experimentally generate a large-scale multiqubit entangled state and experimentally implement large-scale quantum computation.2,Realization of the quantum state transfer and quantum swap gate with atomic ensembles via the dipole blockade mechanism. First, we propose a scheme to realize the quantum state transfer base on the dipole-dipole interaction between two adjacently atomic ensembles. Next, we propose a scheme to realize quantum swap gate with auxiliary atomic ensemble. In our schemes, the qubit is encoded by atomic ensemble, where a large number of atoms help to suppress the negative impact of decoherence on an information stored in atomic ensemble. Our protocols are possible to realize in the current experimental condition.