Research On Optical Quantum Fredkin Gate And GHZ States Analyzer Based On Weak Cross-Kerr Medium

Quantum information processing which includes quantum communication and quantum computation,is an interdisciplinary combining with quantum mechanics with information science.It can not only ensure secure transmission,efficient storage and operation of information,but also solve tasks can't be accomplished by the classical communication and classical computers.As photons are easy to be prepared,controlled,and not sensitive to the variation of the external environment,they are usually used as carriers of quantum information.However,it is difficult to perform interaction between photons.This is one of the main obstacle in the development of optical quantum information processing.By weak cross-Kerr medium,the nonlinear interaction between photons can be implemented.In this dissertation,we design a new optical quantum Fredkin gate and an improved GHZ states analyzer based on weak cross-Kerr medium.Firstly,we briefly overview the quantum information processing,and introduce the development of quantum communication and quantum computation.Then the principles of quantum mechanics,i.e.the unknown quantum state non-cloning theorem,the Heisenberg's uncertainty principle and quantum state evolution hypothesis,are briefly presented.The Fock states,coherent states and linear optical elements related to quantum optics are introduced.The weak cross-Kerr nonlinearity is also discussed in detail.Secondly,we propose optical quantum circuits of a controlled path gate and a quantum Fredkin gate schemes based on the weak cross-Kerr nonlinearity respectively.The working process is presented and the success rate of the two schemes are analyzed in detail.The results show that the success probability of the controlled path gate and quantum Fredkin gate using the weak cross-Kerr medium is close to 100%.In their schemes,the homodyne detection is carried out on the coherent state after the interaction with photons,and then the corresponding classical feed-forward operations are performed according to different measurement outcomes,so quantum logic gates are realized.At the same time,we also briefly present an optical quantum switch unit based on linear optical elements.All modules of the optical quantum switch unit are improved,so that its success rate is greatly improved.Thirdly,based on the analysis of the existing GHZ states analyzers,a general polarization-coded GHZ states analyzer based on the weak cross-Kerr medium is proposed.We first determine the category of the input GHZ state by using the weak cross-Kerr nonlinearity combined with the homodyne detection and classical feed-forward operations,and then determine the specific form of the input GHZ state by single photon detectors,which can completely distinguish the GHZ states.In this paper,the theoretical analysis of the three-photon polarization-coded GHZ states analyzer is carried out,also extended to the multiphoton scenario.In addition,we propose a measurement-device-independent quantum key distribution(MDI-QKD)protocol with three-photon GHZ states analyzer.Finally,we summarize the thesis,and prospect the further research.In the proposed scheme of the optical quantum switch unit,the success rate of quantum state fusion gate is only 1/8,and its core is still composed of linear optical elements.Therefore,the next step is to construct the quantum state fusion gate based on the weak cross-Kerr medium,and make its success probability reach 100%.For the measurement-device-independent quantum key distribution protocol implemented by the three-photon GHZ states analyzer,we haven't analyze its security and the key rate.So the next step is to prove the security of the protocol and analyze its key rate.