Preparation And Protection Of Quantum Entanglement Under Noise Environment

The interaction between the quantum system and the environment will degrade the coherence of the open quantum system,as a result,the quantum entanglement is destroyed and the practical role of quantum entanglement in the quantum information field is limited.Therefore,a lot of researchers have been working on how to protect quantum coherence in recent years.Lots of methods have been proposed.This article based on cavity-atom system mainly focuses on the protection ability of weak measurement schemes and dynamics decoupling on quantum systems in a dissipative environment.Firstly,the dynamic evolution of the system are discussed by solving the master equations in the Markovian environment.Subsequently,the protective effect of weak measurement scheme and dynamic decoupling scheme on the entanglement of atoms is analyzed in the Markov environment.Result show that the longer concurrence stays in the maximum,the closer p is to zero.Although the weak measurement scheme can increase the maximum of concurrence,it is only suitable for finite-temperature environment.With evolution,the concurrence under the protection of weak measurement scheme will decay rapidly,based on the protection of the decoupling scheme,the rate of degradation of concurrence slow down.The entanglement between two distant atoms is successfully established by Bell measurements when atomic dissipation exists in non-Markovian environments.In the absence and presence of atomic dissipation,the analytical result of the wave function under protection of the decoupled sequence by solving the Schrodinger equation is obtained,the protection effects of the weak measurement scheme and the dynamic decoupling method is analyzed in detail.Result show that weak measurement scheme can increase the maximum of entanglement,but it can not suppress the memory effect of non-Markovian environment.However,the dynamics decoupling scheme can suppress the sudden death of entanglement,but it can not increase the maximum of concurrence.The advantages and disadvantages of the two schemes are complementary.Finally,a protection scheme called composite scheme is proposed,consisted of the weak measurement scheme and the dynamic decoupling method.In the Markov environment,composite scheme can make the entanglement stay stable for a long time through the composite scheme.The effects of utilizing two schemes alone is not satisfactory when atomic dissipation exists in non-Markovian environments.The composite protection scheme can protect quantum system resisting noise environment more effectively which provides a theoretical reference for the protection of high-dimensional entanglement.