Frequency Conversion Of An Entangled State And Experimental Generation Of Genuine Four-partite Entangled States With TTPC For Continuous Variables

In quantum information and quantum computation, the information process and transfer are achieved by use of quantum mechanics systems. The study of quantum information and quantum computation not only has extensively potential applications in future information technology, but also provides us a powerful tool for deeply understanding the fundamental principles of quantum mechanics.The quantum entanglement plays a very important role in quantum computation and quantum information process. It is a nature resource for the development of quantum information science. The generation of the multi-partite entanglement states is a premised condition for implementing quantum computation and quantum information networks, and the frequency conversion of the optical entangled states is one of the key technologies to perform quantum information storage and exchange. During my Ph. D period, I studied the frequency conversion of continuous variable entangled states theoretically. Then,. I and my colleagues experimentally produced a new type of four-partite entangled states named TTPC state. Finally, I designed the schemes to realize quantum logic gates based upon Cluster and TTPC four-partite entangled states, which provide useful references for experimentally implementing the quantum computation of continuous variables.The main contents of the thesis are as following:1 The quantum characteristics of sum-frequency process in an optical cavity for implementing the frequency conversion of an entangled state is analyzed. Our calculation proved that the quantum properties of the signal optical beam can be maintained after its frequency is conversed during the intra-cavity nonlinear optical interaction. The frequency-conversed output signal beam is still in an entangled state with the retained other half of the initial entangled beams. The resultant quantum correlation spectra and the parametric dependences of the correlations on the initial squeezing factor, the optical losses and the pump power of the sum-frequency cavity are calculated. The proposed system can be used in quantum communication network and the calculated results can provide direct references for the design of experimental systems.2 We experimentally generate a new type of continuous variable genuine four-partite entangled states, the quantum correlation property of which is different from that of the four-mode GHZ and cluster states. So far, there is no any qubit counterpart to be proposed. The criterion inequalitites for detecting the full inseparability of the entangled states are deduced, in which all parameters are experimentally measurable. In each of the criterion inequalities for the new presented CV genuine four-partite entangled state, the amplitude and phase quadrature correlation variances totally consisting of three-party combination from the four entangled modes are involved, which is different from that included some two-party correlations of amplitude and phase quadratures of optical modes for the GHZ and Cluster states, thus we named it the four-partite entangled state with total three-party correlation (TTPC), briefly, TTPC state.3 Theoretically proved that the TTPC four-partite entangled states can be used to realize the CNOT logical operation. We have suggested an experiment scheme, and the experimental research is going on.4 The experimental system to realize the one-way quantum logical operations based on the linear four-partite cluster entangled state is designed. The possibly experimental results under the influence of the quantum noise are calculated through the computer simulation.The completed creative works are as follows:1 We theoretically prove that the initial EPR entanglement between the amplitude and phase quadratures of entangled beams can be preserved after the frequency of one of the beams is conversed via a nonlinear interaction of sum-frequency generation(SFG) in an optical cavity. The dependences of the resultant correlation fluctuation spectra on the parameters of SFG system are calculated, which may be a useful reference for the design of quantum communication systems.2 We experimentally generate a new type of continuous variable genuine four-partite entangled states. Up to now, there is no any qubit counterpart to be proposed. We deduce the criterion inequalitites for detecting the full inseparability of this entangled state. The measured correlation variances among the quadratures of the prepared entangled states satisfy the sufficient requirements for the fullinseparability.3 We propose the experimental schemes to realize the quantum logical operationsusing the two types of continuous variable genuine four-partite entangled states,linear cluster states and TTPC states, and prove the feasibility of these proposedschemes.