Study On The Entanglement Concentration Of Three-particle GHZ State And W State

In recent years,with the gradual development of science and technology,quantum informatics has begun to attract the attention of many researchers.Quantum informatics includes quantum information and quantum computing,which are based on entangled states.The carrier of quantum information is the microscopic quantum state and the manipulation of the quantum state satisfies the basic principles of quantum mechanics.Therefore,the encoding,manipulation,transmission and decoding of quantum information are greatly different from the traditional classical informatics.In classical informatics,the operation of information still satisfies the laws of classical mechanics.With the special properties of quantum mechanics,quantum information technology can have more powerful capabilities than the corresponding classical techniques.Quantum information technology can realize absolutely safe quantum communication,and can also solve the computational problems that are difficult to be accomplished in classical computers.Quantum information technology represents the strategic direction of the future development of information technology,and is the focus of the next generation of secure communication systems in the world.It is likely to have an inestimable impact on the economic development of human society.When accomplishing the various quantum information tasks,the maximally entangled states are required in general as the entangled channel.It is usually prepared locally and then distributed or transmitted to remote receivers.However,the transmission process is done through the classical channel,and there is environmental noise around the channel,which leads the maximally entangled states to occurring de-coherence and eventually become partially entangled states or mix states.At the same time,the reduction of entanglement affects the security and fidelity of quantum communication protocols.In order to overcome this problem,entanglement purification and entanglement concentration techniques came into being.Generally speaking,when the initial state is partially entangled state,the maximum entangled state can be extracted from the subsystem using entanglement concentration.When the initial state is the mixed state,the entanglement purification can improve the fidelity of the mixed state.In this paper,the main focus is on two special multi-particle entangled states,that is GHZ state and W state.The paper first summarizes the concentration protocols proposed by some researchers,and finally introduces our own protocols.The existing entanglement concentration protocols need to be completed using the parity check gate,three different forms of parity check gates are introduced by us in the article.The first one is composed of two polarization beam splitters and its structure is the simplest and most practical.The second one is comprised of a quantum non-destructive detector using a cross-Kerr nonlinear effect.The last one is composed of quantum dot and microcavity coupling systems and needs the help of single photon.With the idea of iterative concentration,the success probability of the protocols is greatly increased.This has great practical value for long-distance quantum security communication,and these protocols have a certain feasible in experiment.