The Decoherence Of The Double-mode Multi-photon Entangled State And The Polyatomic System

Quantum information science is a new sphere found on the fundamental principle of quantum mechanics,which consist of quantum computation and quantum communication mainly.Quantum computation is more superior to classical computation,because quantum computation makes use of important physical resource of quantum information science-quantum coherence and superposition.However,that quantum systems interact with surrounding environment inevitably leads to entanglement between quantum states and environmental states and finally leads to quantum decoherence which destroy quantum coherence of the states.In other words,quantum decoherence reduces coherent effect or evanishes it absolutely.First of all,in the paper we review the foundation of quantum decoherence including basic knowledge of quantum system and environment,expression of decoherence,formal theory of decoherence,master equation describing the process of decoherence and several entropys measuring the degree of entanglement of quantum states.In chapter two of this paper we discuss the decoherence course and characteristics of the two-mode multi-photon entangled state.According to the master equation of the two-mode multi-photon entangled state coupled with an environment,we obtain the two-mode multi-photon entangled mixed state under decoherence.After that we give a new degree of mixing,and calculate the degree of mixing of the mixed state.Then we calculate the concurrence of the two-mode multi-photon entangled mixed state.For the past few years,research scholars take an interest in the decoherence characteristics of many-body quantum systems.In this paper we study the decoherence characteristics of the polyatomic system.According to the master equation of the open systems,we give both the master equation of the polyatomic system coupled with the environment and the exact solution of this master equation by making use of super operator Lie algebra.After that we choose the W state that has a specific entanglement distribution as the initial state of the polyatomic system,and give the global entanglement of the W state under decoherence.